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Satellite-tracking of adult bumphead sunfish, Mola alexandrini, revealed long-distance latitudinal migration patterns covering thousands of kilometers. Horizontal and vertical movements of four bumphead sunfish off Taiwan were recorded with pop-up satellite archival tags in 2019–2020. Two individuals moved northward and traveled to Okinawa Island and Kyushu, Japan and two moved southwards; crossing the equator, to Papua New Guinea and New Caledonia. During daytime, bumphead sunfish descended below the thermocline and ascended to mixed layer depths (MLD) during nighttime. The N–S migrants, however, demonstrated different habitat utilization patterns. Instead of using prevailing currents, the northward movements of sunfish cohorts exhibited extensive use of mesoscale eddies. Fish in anticyclonic eddies usually occupied deeper habitats whereas those in cyclonic eddies used near-surface habitats. On northward excursions, fish spent most of their time in regions with high dissolved oxygen concentrations. Southward movement patterns were associated with major currents and thermal stratification of the water column. In highly stratified regions, fish stayed below the thermocline and frequently ascended to MLD during daytime either to warm muscles or repay oxygen debts. These results for bumphead sunfish present important insights into different habitat use patterns and the ability to undergo long-distance migrations over varying spatial-temporal scales and features.

20 pages, 3 tables, 5 figures.-- Samantha Andrzejaczek ... et al.-- Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC), Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements, Data analysis was funded by the Bertarelli Foundation through the Marine Science program through grants to D.J.C., B.A.B., and S.A. D.J.C. is also funded through Research England, UK. S.A. and B.A.B. thank the Moore Foundation and the Packard Foundation. F.G.-M. thanks the Instituto Politecnico Nacional for fellowships (COFAA, EDI). S.B.W. thanks funding from the Darwin Initiative (DPLUS046). A.D.M.D. acknowledges funding from the Research and Conservation Budget at Georgia Aquarium, including philanthropic gifts from several anonymous donors. K.F. acknowledges funding from the Rolex Awards for Enterprise and the Whitley Fund for Nature

Billfishes are considered important fishery resources and the identification of aggregation sites is imperative for proper management. Here we present evidence of a seasonal aggregation site for juvenile istiophorid billfishes in southern Brazil. We discuss the results as they relate with the need for management at a local scale and participatory monitoring with artisanal fishing communities as a way to ensure access to data on the occurrence and population status in the long term.

Bycatch in pelagic longline fisheries threatens the viability of some seabird populations and reduces fishing efficiency. The mass of a branchline fishing weight and its distance from the hook significantly explain seabird catch risk during setting and hauling. We surveyed Hawaii tuna longline fishers to obtain their perspectives on the practicality, safety and economic viability of alternative designs which place weights adjacent to hooks instead of conventional designs with weighted swivels attached 0.6 m from the hook. We conducted experimental fishing to explore the commercial viability of a combination weighted swivel attached to the eye of the hook. We used a Bayesian random effects meta-analytic regression modeling approach to estimate pooled expected species-specific log relative risk of capture on conventional, as opposed to experimental, branchlines. There were significant decreases in catch rates on experimental branchlines of 54% (95% highest posterior density interval [HDI]: 34.3 to 73.8) for retained species and 28% (95% HDI: -7.5 to 93.3) for discarded species. For about 10% of experimental weighted hooks, the point of the hook tangled on the swivel, likely contributing to lower catch rates and making it more difficult for crew to coil branchlines. We identify possible factors explaining why the experimental gear reduced catch rates. The study demonstrates the benefits of stakeholder scoping to determine bycatch mitigation options with the highest promise for practicality, economic viability and safety, as well as benefits of conducting a pilot study to assess commercial viability to determine if a full experiment to assess bycatch mitigation efficacy is warranted.

This paper presents the first application of pop-up satellite archival tags (PSATs) to giant trevally (Caranx ignobilis) in a "no-take" marine protected area (MPA) comprising in a major reef system in the South China Sea (Dongsha Attol National Park). In order to determine appropriate management strategies in an around the MPA and to delimit stock boundaries to help restore populations, fundamental ecological information is required on movement patterns, habitat preferences and home range. In total 10 giant trevally were tagged from May 2016 to September 2018. Eight tags reported and remained affixed from 17 to 243 days and linear displacements ranged from 26 to 826 km from deployment to pop-up locations. Fish were mainly confined to the mixed-layer but occasionally made deeper descents (~50 -60 m) during nighttime and the distributions of time spent at depth (~0 - 67 m) and temperature (21.5 - 35.4°C) were significantly different between daytime and nighttime but the transitions were not pronounced. Most probable tracks calculated from a state-space Kalman filter suggested site-fidelity and/or cyclic N-S dispersal patterns possibly related to spawning or foraging as about half of the pop-up locations were within ~100 km of the tagging location. Given these findings and implications, it is possible that giant trevally may need to be managed at small spatial scales to preserve genetic diversity. Additional tagging studies, however, using genetic data and conventional tags to maximize cost-benefit and augmented with a sub-set of PSATs, will be required to test this hypothesis at a higher level of statistical power.

To gauge the effectiveness of supplementing native populations of dolphinfish Coryphaena hippurus, we compared farm-raised and wild fish in terms of their horizontal and vertical movement patterns, habitat preferences and thermal niche using pop-up satellite archival tags (PSATs) deployed in two disparate locations: the sub-tropical southeastern coast of Taiwan (wild, n = 4), and temperate Kagoshima Bay, Japan (farm-raised, n = 3). Tagged fish were tracked for periods of 7–40 days, reached depths > 100 m, and experienced temperatures of 15–30 °C in Taiwan, and 20–23 °C in Kagoshima Bay. Fish tagged in Taiwan made primarily northward movements during early summer but changed to a southward course in early winter. In Kagoshima Bay, tagged fish undertook southward excursions along the coast and movements were confined to the bay. Dolphinfish spent > 50% of their time near the surface and made more extensive vertical movements during the night than during the day; vertical movements were largely confined to the mixed layer. Depth distributions appeared to be limited by a Δ6 °C change in temperature relative to sea surface temperature (i.e., > 90% of movements were within 6 °C of the warmest water available).

To gain a better understanding of the trophic ecology of Pacific blue marlin Makaira nigricans off eastern Taiwan, nitrogen and carbon stable isotopes (δ15 N and δ13 C) and Bayesian mixing models were used to explore trophic dynamics and potential ontogenetic feeding shifts across M. nigricans of different size classes. Makaira nigricans samples from east of Taiwan (n = 213) and Palau (n = 37), as well as their prey (n = 70), were collected during 2012 and 2013. Results indicated increases in δ15 N with size, with values of larger size classes (> 200 cm eye-to-fork length; LEF ) significantly higher than those 200 cm LEF had the highest estimated trophic position (4.44) and also exhibited ontogenetic changes in trophic position. Large M. nigricans fed more on dolphinfish Coryphaena hippurus and hairtail Trichiurus lepturus, while smaller M. nigricans consumed smaller forage fish (e.g., moonfish Mene maculata) and cephalopods. These changes may relate to greater swimming speeds and vertical habitat use in larger M. nigricans, allowing capture and consumption of larger prey items at higher trophic positions. The high trophic level of M. nigricans east of Taiwan confirms its important role as an apex predator in marine food webs and how ecological role changes with size.

Robust assessments of the effects of fishing require accounting for components of fishing mortality, including post‐release fishing mortality (Fᵣ). Random‐effects meta‐analysis synthesized Fᵣ in seven pelagic shark species captured, tagged and released with 401 pop‐up satellite archival tags compiled from 33 studies and three gears (longline, purse‐seine, rod & reel). The majority of Fᵣ outcomes occurred within days of release, and the summary effect size for Fᵣ was 0.27 [95% CI: 0.19–0.36], ranging from a low pooled effect size of 0.17 for blue shark (Prionace glauca, Carcharhinidae) to 0.38 (silky shark, Carcharhinus falciformis, Carcharhinidae). Fᵣ rates in blue shark were consistent over dissimilar spatial and temporal scales, and results from earlier meta‐analysis were replicated, which is the most powerful way to authenticate results. Condition at tagging was a strong predictor, and dichotomized survival outcomes in silky shark and no sex‐, size‐, location‐ or gear‐specific Fᵣ rates were demonstrated. Meta‐analyses and sensitivity analyses indicated exposure to risk factors and conditions whilst caught on the gear probably had the largest explanatory effect on Fᵣ, rather than stressors incurred during handling and release. Records from 549 tagged istiophorid billfishes (six species, three gears, 43 studies) demonstrated they are more robust to stressors sustained during capture, handling and release than pelagic sharks. Findings from previous meta‐analysis on Fᵣ rates in white marlin (Kajikia albida, Istiophoridae) were replicated. Synthesized Fᵣ rates enable prioritizing approaches to mitigate by‐catch fishing mortality, to improve the quality of stock and ecological risk assessments and to expand our knowledge of factors influencing trophic structure.

Bycatch in fisheries can have profound effects on the abundance of species with relatively low resilience to increased mortality, can alter the evolutionary characteristics and concomitant fitness of affected populations through heritable trait-based selective removals, and can alter ecosystem functions, structure and services through food web trophic links. We challenge current piecemeal bycatch management paradigms, which reduce the mortality of one taxon of conservation concern at the unintended expense of others. Bycatch mitigation measures may also reduce intraspecific genetic diversity. We drew examples of broadly prescribed ‘best practice’ methods to mitigate bycatch that result in unintended cross-taxa conflicts from pelagic longline, tuna purse seine, gillnet and trawl fisheries. We identified priority improvements in data quality and in understanding ecological effects of bycatch fishing mortality to support holistic ecological risk assessments of the effects of bycatch removals conducted through semi-quantitative and model-based approaches. A transition to integrated bycatch assessment and management that comprehensively consider biodiversity across its hierarchical manifestations is needed, where relative risks and conflicts from alternative bycatch management measures are evaluated and accounted for in fisheries decision-making processes. This would enable managers to select measures with intentional and acceptable tradeoffs to best meet objectives, when conflicts are unavoidable.

Derelict abandoned, lost and discarded fishing gear have profound adverse effects. We assessed gear-specific relative risks from derelict gear to rank-order fishing methods based on: derelict gear production rates, gear quantity indicators of catch weight and fishing grounds area, and adverse consequences from derelict gear. The latter accounted for ghost fishing, transfer of microplastics and toxins into food webs, spread of invasive alien species and harmful microalgae, habitat degradation, obstruction of navigation and in-use fishing gear, and coastal socioeconomic impacts. Globally, mitigating highest risk derelict gear from gillnet, tuna purse seine with fish aggregating devices, and bottom trawl fisheries achieves maximum conservation gains. Locally, adopting controls following a sequential mitigation hierarchy and implementing effective monitoring, surveillance and enforcement systems are needed to curb derelict gear from these most problematic fisheries. Primary and synthesis research are priorities to improve future risk assessments, produce the first robust estimate of global derelict gear quantity, and assess the performance of initiatives to manage derelict gear. Findings from this first quantitative estimate of gear-specific relative risks from derelict gear guide the allocation of resources to achieve the largest improvements from mitigating adverse effects of derelict gear from the world’s 4.6 million fishing vessels.

\ₑprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/faf.12631; For many years, tremendous effort has been dedicated to developing new industrial tuna fisheries, while their adverse impacts on threatened marine species have received relatively little attention. In tuna fisheries, bycatch is the major anthropogenic threat to marine megafauna in general, particularly sharks. Research on the development of gear technology for bycatch reduction and potential mitigation measures helped tuna Regional Fisheries Management Organizations adopt bycatch reduction management measures. After reviewing past research on the development of mitigation measures for pelagic longline and tropical purse seine fisheries based on pelagic species' behaviours, we describe promising new approaches integrating recent technological breakthroughs. New innovations include autonomous underwater vehicles carrying cameras along with miniaturized sensors, aerial drones, computer simulation of fishing gear geometry, environmental DNA assays, computer visualizations and deep learning. The successful application of such tools and methods promises to improve our understanding of factors that influence capture, escape and stress of caught species. Moreover, results emerging from recent ethological research explaining the power of social connection and learning in the “fish world” such as social learning from congeners, habituation to deterrents, and how past fishery interactions affect responses to fishing gear should be taken into account when developing technical mitigation measures.

To learn about the movement patterns of bigeye tuna in eastern Taiwan, pop-up satellite archival tags were attached on five tuna ~55 kg and prematurely detached and popped-up after 32 to 132 days-at-liberty. Two tags were physically recovered and provided fine-scale data archiving the full 47 and 132 days-at-liberty. The deepest descent recorded was 1,292 m and the coldest temperature visited 2.7°C. During daytime, the fish spent the majority of time above 400 m at temperatures from ~10 - 25°C and at nighttime; residency was largely confined to the mixed-layer from the surface to ~100 m. Vertical movements traversing through the thermocline during the daytime are based on physiological constraints and/or rapid directional changes conducive for optimal search strategies that increases the chances of prey encounters. Bigeye tuna appear to follow the diel vertical movements of prey organisms comprising the deep sound scattering layer to exploit them as a resource.

Place: Dordrecht Publisher: Springer WOS:000555361400001; International audience; Fisheries can profoundly affect bycatch species with 'slow' life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait's chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4-59%) and 60% (95% HDI: 44-76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of a significant overall estimate of relative capture risk for pelagic shark species combined but significant effect for blue sharks suggests there is species-specific variability in bait-specific catch risk within this group. A qualitative literature review suggests that tunas and istiophorid billfishes may have higher catch rates on squid than fish bait, which conflicts with reducing marine turtle and blue shark catch rates. The findings from this synthesis of quantitative and qualitative evidence support identifying economically viable bycatch management measures with acceptable tradeoffs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries.

Accounting for components of fishing mortality, including post-release mortality (Fr), is necessary for robust assessments of the effects of fishing. Forty-eight blue (Prionace glauca) and 35 silky sharks (Carcharhinus falciformes) were tagged with pop-up satellite archival tags to monitor Fr rates from pelagic longline vessels in the western tropical Pacific Ocean. There is a paucity of Fr studies at low latitudes and identifying factors that significantly explain Fr is critical for understanding fishing mortality. Mean Fr rates were 0.17 [95% CI 0.09–0.30] for blue shark and 0.20 [95% CI 0.10–0.36] for silky shark. When it occurred, Fr was acute with 87% of mortalities within 2 days of release. Several prognostic operational, environmental, biological and handling variables were evaluated to assess their influence on survival outcomes. Using Kaplan–Meier survival curves, logistic regression, accelerated failure time and Cox proportional hazards models to screen variables, the only significant prognostic or risk variable was health condition at haulback. There was close correspondence (~ 83% accuracy) between condition at capture and survival outcomes. Reliable methods to classify at-vessel condition represent an inexpensive and simple metric for estimating both Fr and at-vessel (Fc) mortality rates. Examining Fc rates in detail in longline fisheries using capture information on depth, temperature and dissolved oxygen that may act in synergy with condition code and hooking duration is a research priority. Results suggest that a large proportion of shark survive following release and that Fr rates can be increased by improving the haulback condition of captured sharks.

Pelagic fisheries can have profound effects on ecosystem structure and functioning, affecting ecosystem services, including fisheries production, and threaten vulnerable bycatch species. Controlling hook size could manage the species- and size-selectivity and survival of target and incidental catch. To test this hypothesis, we conducted experimental pelagic longline fishing in the western tropical Pacific testing a control hook and two hooks with wider minimum widths. Data such as catch, length and condition were fit to response-specific Bayesian geo-additive generalized additive and linear mixed regression models. Model fits were assessed using posterior predictive check tests. Catch rates of both retained and discarded species were significantly higher on medium hooks. Target tuna species were significantly larger and had significantly higher at-vessel survival rates on wider hooks. Significantly larger billfishes, also market species, were caught on narrowest hooks. These effects of hook width on length and survival, however, are a much smaller determinant of economic value of the catch than effects on catch rates. If input controls are limiting, then, relative to medium hooks, continued use of narrowest hooks would maintain current economic viability without causing a significant increase in discard catch levels, including of vulnerable sharks. If market species output controls are limiting, because the ratio of retained to discarded catch on medium hooks was greater than on narrowest hooks, medium hooks would generate lower discard levels. Further research assessing single-factor effects of longline hook width is needed to support robust meta-analyses that account for fishery-specific effects.

Black marlin (Istiompax indica) are large, highly mobile, apex pelagic predators of tropical and subtropical oceans with high economic importance in western North Pacific fisheries. To assess the ontogenetic trophic ecology of black marlin in the western North Pacific Ocean, the stable isotopic composition of 177 black marlin muscle samples (87–383 cm, eye-orbit fork length (EFL); 33–447 kg, body weight) were examined for ontogenetic shifts and seasonal variability in trophic position. δ15N and δ13C values for black marlin ranged from 9.7 to 14.5‰ and −18.5 to −15.2‰, respectively, and δ15N values were positively correlated with size. δ15N and δ13C values varied across seasons, with highest δ15N values in autumn. Based on trophic position estimates and Bayesian mixing models, large black marlin (>250 cm EFL) occupied a higher trophic position (4.8) and fed on more mesopelagic prey (e.g. hairtail, Trichiurus lepturus) compared to smaller individuals, which were estimated to feed more on forage fish and squids as well as hairtail. These results suggest that the trophic position of black marlin varies across life-history stages and seasons, possibly reflecting seasonal movements in surrounding pelagic ecosystems. Trophic level estimates highlight the important ecological role of black marlin as a top predator in pelagic ecosystems, and indicate potential regional importance of mesopelagic fishes in diets.

Black marlin ( Istiompax indica ) is a highly migratory apex predator distributed widely throughout the Pacific and Indian Oceans, with seasonal densities occurring in the East and South China Seas and near Taiwan. The peak seasonal presence of black marlin in eastern Taiwan (September to November) has led to the development of a commercially important harpoon fishery that specifically targets this aggregation. The harpoon fishery provides relatively easy access to black marlin for tagging research to monitor their movement patterns with pop-up satellite archival tags (PSATs). Nine black marlin were tagged from February 2011 to March 2012 with PSATs that acquired depth, temperature and ambient light-level data. PSATs remained affixed for a median 95 days (average 132 days ± 38 SE, range: 10–360 days) which are the highest documented PSAT retention statistics for any istiophorid billfish. No post-release mortalities occurred in these data and the harpoon method of PSAT application, as well as an improved anchor, may promote longer retention times by tagging fish that are not subjected to stress or injury associated with prolonged fishing bouts or handling. Linear displacements ranged from 567 to 1226 km from deployment to pop-up locations with speeds of 3.1–122.6 km day −1 (average: 6.4 km day −1 , 0.3 km h −1 ). Most probable tracks calculated by the state-space Kalman filter, augmented with sea surface temperature (SST), suggested that black marlin undergo dichotomous seasonal movement patterns: fishes tagged in spring and summer moved in a northerly direction to the East China Sea and those tagged in winter moved in a southerly direction to the South China Sea. Estimated track models during March–April for tagged fish in southwestern Taiwan coincided with known spawning activity in this vicinity though the tracks and vertical data were not sufficiently detailed to discriminate this putative behaviour. Diving depths ranged from the surface to ∼258 m and ambient water temperatures occupied ranged from 30.3 °C to 14.5 °C. The distribution of time spent at depth and temperature was significantly different between daytime and nighttime diving activity. Tagged black marlin spent the majority of daytime in the surface mixed-layer to ∼50 m and exhibited occasional basking behaviour; and at nighttime, they were confined almost exclusively to the surface to ∼20 m. Depth distribution appeared to be limited by an 8 °C change in water temperature relative to the warmest water (ΔSST). In the context of regional fisheries management and stock assessments, our study reports the first tagging data of black marlin in Southeast Asia and it will be especially important to compare diving behaviour patterns with other specimens tagged using other fishing methods to discern differences. Like many previous electronic tagging studies on istiophorid billfish in the Pacific, the data suggest that the majority of habitat for black marlin in Taiwan may be adequately described by two dimensions (this species spends most of their time in the surface mixed-layer).

Meta-analysis (inverse-variance, random-effects model) involving 46 studies was used to estimate the effect size of postrelease mortality (Fr) in six istiophorid billfish species (black marlin (Istiompax indica), blue marlin (Makaira nigricans), longbill spearfish (Tetrapturus pfluegeri), sailfish (Istiophorus platypterus), striped marlin (Kajikia audax), and white marlin (Kajikia albida)) following release from recreational, longline, and harpoon fishing gears. The studies involved 400 reporting pop-up satellite archival tags and 64 reporting acoustic (ultrasonic) tags. Despite fish being captured, tagged, and released under widely disparate conditions, locations, and gear types, Fr was homogeneous among species. Variability in Fr was principally due to random sampling error within studies with no evident patterns. Fifteen studies (33% of tags) indicated no mortality, and the overall summary effect size for Fr was 13.5% (95% CI: 10.3%–17.6%). Since the random-effects model decomposed to a fixed-effect model when the between-studies variance T2 = 0.00, results were confirmed using exact nonparametric inferential tests and sensitivity analyses. Our results support earlier findings in the Atlantic and substantiate the majority of istiophorid billfish survive when released from recreational and longline fishing gear, clearly implying catch-and-release as a viable management option that permits fishing activity while protecting parental biomass and the fishery.

There are few reliable estimates of post-release mortality for sea turtle species because of the many challenges and costs associated with tracking animals released at sea. In this study, the likelihood of sea turtle mortality as a result of interactions with longline fishing gear was estimated based on satellite telemetry data, such as the number of days an animal was successfully tracked, or days at liberty (DAL) and dive depth data, as well as anatomical hooking locations. Pop-up satellite archival tags were deployed on 29 loggerhead sea turtles (Caretta caretta) caught by the North Pacific US-based pelagic longline fishery operating from California and Hawaii between 2002 and 2006. Loggerhead turtles were catagorized by observers as shallow-hooked (55%) if the animal was entangled in the line or the hook was in the flipper, jaw or mouth and could be removed, or deep-hooked (45%) if the hook was ingested and could not be removed. The vertical movements of turtles were used to infer potential mortalities. Of the 25 tags that reported data, the DAL ranged from 3 to 243 days (mean = 68 days). The DAL was shorter (by nearly 50%) for shallow-hooked (mean = 48 days, range: 3 to 127) compared to deep-hooked turtles (mean = 94 days, range: 5 to 243), but these changes were not statistically significant (P = 0.0658). Although aspects of these analyses may be considered speculative, these data provide empirical evidence to indicate that deep-hooking is not linked to shorter DAL. DAL, anatomical hooking location, and gear removal were evaluated with inferences about the extent of injuries and rates of infection to estimate an overall post-release mortality rate of 28% (95% bootstrap CI: 16–52%). This range of estimates is consistent with those used to shape some US fisheries management plans, suggesting that conservation goals are being achieved at the expected level and ideally striking a balance between the interests of industry and those of protected species. Copyright © 2013 John Wiley & Sons, Ltd.

Spatial and temporal trends of sailfish catch rates in the southwestern and equatorial Atlantic Ocean in relation to environmental variables were investigated using generalized additive models and fishery-dependent data. Two generalized additive models were fit: (i) ‘spatio-temporal’, including only latitude, longitude, month, and year; and (ii) ‘oceanographic’, including sea surface temperature (SST), chlorophyll-a concentration, wind velocity, bottom depth, and depth of mixed layer and year. The spatio-temporal model explained more (average ~40%) of the variability in catch rates than the oceanographic model (average ~30%). Modeled catch rate predictions showed that sailfish tend to aggregate off the southeast coast of Brazil during the peak of the spawning season (November to February). Sailfish also seem to aggregate for feeding in two different areas, one located in the mid-west Atlantic to the south of ~15°S and another area off the north coast of Brazil. The oceanographic model revealed that wind velocity and chlorophyll-a concentration were the most important variables describing catch rate variability. The results presented herein may help to understand sailfish movements in the Atlantic Ocean and the relationship of these movements with environmental effects.

Pop-up satellite archival tags (PSATs) are used to chronicle or 'archive' the habitat preferences, horizontal and vertical movements, fishery interaction, and post-release mortality rates of a variety of pelagic animals. Though PSATs are valuable research tools, lower-than-expected reporting rates, early detach- ment, and incomplete data return remain problematic. These issues were quantified by analysis of reporting rates, retention times (i.e. the time period PSATs re - mained attached), and the quantity of depth, tempera- ture, and geolocation data returned from 731 PSAT deployments on 19 species in the authors' database and 1433 PSAT deployments on 24 species taken from 53 published articles. The reporting rate of PSATs de - ployed by the authors (0.79, 95% CI = 0.76 to 0.82) was not significantly different from the reporting rate calcu- lated from published studies (0.76, 95% CI = 0.74 to 0.78). PSAT reporting rates were lowest in species undertaking large (~1000 m) vertical excursions (logis- tic regression, p = 0.006), and reporting rates have increased significantly over time (p = 0.02), presum- ably because of better PSAT design and construction. Tag retention increased with depth range of the tag - ged species and pop-off latitude (Cox proportional hazards models, p < 0.001), suggesting that pressure (and/or temperature), biofouling, and wound infection at the insertion site of the PSAT's anchoring device influenced this parameter. The quantity of data re - turned by Argos satellites was affected by tag produc- tion year, programmed pop-up period, depth range, and manufacturer. Species-specific reporting rates were used to make recommendations for future PSAT sampling designs.

Swordfish are highly specialized top-level predators that have been challenging to study. In this paper, data from 31 pop-up satellite archival tags attached to swordfish from (i) the eastern Pacific, (ii) central Pacific, and (iii) western North Atlantic-Caribbean were analyzed. Common across locations was a pronounced diel vertical pattern with daytime hours spent primarily below the thermocline and nighttime hours spent in warmer waters, close to the surface. One exception to this pattern was periodic daytime basking events which were most common in cooler waters off California. Maximum daytime depths were significantly correlated with light penetration as measured by the diffuse attenuation coefficient at 490 nm. Temperature did not appear to influence daytime depths, and swordfish tolerated both extremely low temperatures (4� C) and rapid and dramatic temperature changes (>20� C). Temperature did appear to influence the nighttime depths in the Pacific where fish typically remained in the surface mixed layer. In contrast, in the warm tropical Atlantic this was not the case, and nighttime depths were much deeper. In all areas, nighttime depth increased around the full moon. Given the parallels between the vertical movement patterns of swordfish and those of the deep sound scattering layer we suggest that swordfish vertical distribution patterns, especially during daytime, are influenced largely by resource availability. At night, when swordfish are typically targeted by fisheries, both ambient light and temperature influence movements. Understanding vertical movement patterns of swordfish can help evaluate gear vulnerability, improve population assessments, and potentially reduce fisheries bycatch.

Sailfish (Istiophorus platypterus) are of substantial economic importance to Taiwan because of their seasonal abundance (April to October, with a peak from May to July) off the island's eastern coast. They are harvested by drift gill nets, set nets, harpoons, and as incidental bycatch by inshore longline fisheries. Although the biology of sailfish has been investigated in eastern Taiwan, there is a paucity of data on movement patterns. Pop-up satellite archival tags (PSATs) were used to study the vertical and horizontal movements of three sailfish in 2008. The fish were tagged near the southeastern coast of Taiwan and linear displacements ranged from 1050 to 1400 km (~ 40 km day− 1) from deployment to pop-up locations and all movements were confined to the East China Sea. Sailfish spent 88% of their time in the upper uniform mixed layer above 50 m, but made more extensive vertical movements during the nighttime ( x ¯ = 60.61 m ± 48.24 SD) than daytime ( x ¯ = 35.21 m ± 35.37 SD). Depths and ambient water temperatures visited ranged from 0 to 214 m and 30.0° to 17.8 °C, respectively. However in all cases, the depth distribution appeared primarily limited by an 8 °C change in water temperature. Diel diving patterns also suggested basking behavior. Sailfish behavior makes them particularly vulnerable to surface fishing gears.

1.This study compared the catch rates of targeted dolphinfish or mahimahi (Coryphaena hippurus), and sea turtles and other fish bycatch in a shallow-set Costa Rican longline fishery using 14/0 circle hooks with and without a 10° offset. The effect of hook offset on hooking location and injury in captured sea turtles, specifically if the hooking was external, in the mouth, or in the esophagus was also evaluated. 2.Results were compared from six trips totalling 33 876 hooks with squid (Dosidicus gigas) used as bait. In total, mahimahi catch-per-unit-effort (CPUE, expressed as number caught per 1000 hooks) was similar between hook types (CPUE∼52). 3.Olive ridley sea turtles (Lepidochelys olivacea) were caught on all 42 sets. In total, 640 olive ridley turtles were caught and released alive. There were no significant differences in the number of sea turtles caught between hooks with and without an offset (CPUE∼19) nor between hook type and anatomical hooking location, suggesting similar levels of injury for turtles caught on each hook type. 4.These data suggest that a 10° offset on 14/0 circle hooks does not confer any selective advantages over hooks with no offset with respect to capture rates of mahimahi, sea turtles, sharks, or pelagic stingrays in a shallow set pelagic longline fishery. Copyright © 2010 John Wiley & Sons, Ltd.

SUMMARYWe developed a 2D heat flux model to elucidate routes and rates of heat transfer within bigeye tuna Thunnus obesus Lowe 1839 in both steady-state and time-dependent settings. In modeling the former situation, we adjusted the efficiencies of heat conservation in the red and the white muscle so as to make the output of the model agree as closely as possible with observed cross-sectional isotherms. In modeling the latter situation, we applied the heat exchanger efficiencies from the steady-state model to predict the distribution of temperature and heat fluxes in bigeye tuna during their extensive daily vertical excursions. The simulations yielded a close match to the data recorded in free-swimming fish and strongly point to the importance of the heat-producing and heat-conserving properties of the white muscle. The best correspondence between model output and observed data was obtained when the countercurrent heat exchangers in the blood flow pathways to the red and white muscle retained 99% and 96% (respectively) of the heat produced in these tissues. Our model confirms that the ability of bigeye tuna to maintain elevated muscle temperatures during their extensive daily vertical movements depends on their ability to rapidly modulate heating and cooling rates. This study shows that the differential cooling and heating rates could be fully accounted for by a mechanism where blood flow to the swimming muscles is either exclusively through the heat exchangers or completely shunted around them, depending on the ambient temperature relative to the body temperature. Our results therefore strongly suggest that such a mechanism is involved in the extensive physiological thermoregulatory abilities of endothermic bigeye tuna.

A longline experiment consisting of 45 paired sets (90 sets total) was carried out to evaluate a technique which maintains target catch rates while reducing non-target catch rates. Control sets were compared to experimental sets which eliminates the shallowest hooks (∼less than 100 m depth). Researchers hypothesized that by eliminating shallow hooks, target catch of deeper dwelling species such as bigeye tuna ( Thunnus obesus ) would be maximized while incidental catch of many other non-target, but marketable epi-pelagic species (e.g. billfish), bycatch (discards) of other fishes and elasmobranchs, and protected sea turtles and marine mammals would be simultaneously reduced. To control for differences in fishing power, gear, and deployment techniques; a single vessel was contracted to perform all 90 paired longline sets (45 experimental sets using no-shallow-hooks and 45 control sets using standard methods). Control sets consisted of longlines that were suspended by floats on typical 30 m long floatlines in catenary-type shapes that fished a range of depths, determined by temperature–depth recorders (TDRs) to be 44–211 m (27.5–11.2 °C). By contrast, elimination of shallow hooks in the upper 100 m of the water column (hereinafter referred to as experimental sets) was achieved by suspending the fishing portion of the mainline on 75-m long, 3 kg weighted vertical sections of mainline suspended by floats on 30 m floatlines. As determined by TDRs, this arrangement ensured that all hooks fished at depths >100 m (103–248 m; 24.8–11.3 °C). Thirty percent of hooks in control sets fished at depths less than 100 m while all hooks on experimental gear fished greater than 100 m. Because many factors influence catchability, longline sets are by nature multivariate, and statistical comparisons were made between the two set types using canonical discriminant analysis (CDA). Except for the depth of shallow hooks, operational characteristics between experimental and control sets were the same. The catch rates of bigeye tuna were similar on the two sets types but the catch rate of sickle pomfret ( Taractichthys steindachneri ) was significantly higher ( p = 0.011) in the experimental sets as compared to control sets. However, statistically fewer wahoo ( Acanthocybium solandri , p = 0.019), dolphinfish ( Coryphaena hippurus , p = 0.008), blue marlin ( Makaira nigricans , p = 0.001), striped marlin ( Kajikia audax , p = 0.018) and shortbill spearfish ( Tetrapturus angustirostris , p = 0.006) were captured on the experimental sets; thus longline interactions and impacts on these species were reduced with the experimental gear. The reason for the differences in catch rates between gear types is likely due to the vertical habitat preferences of the species involved; interactions with epi-pelagic species with shallow distributions in the uniform mixed layer were reduced by deploying hooks greater than 100 m. By logical extension, the experimental gear will also likely reduce interactions with sea turtles. Except for additional lead weights, floats, and floatlines, only slight modification of existing longline fishing gear and methods were required to deploy the experimental gear. The main drawback of this method was the increase in time to both deploy (≈0.5 h) and retrieve (≈2 h) the gear. Knowledge of species vertical distribution patterns can play an important role in modifying fishing gear to reduce bycatch and can also assist managers in regulating fishing practices with a higher degree of likelihood of predicting catch rates and species captured in different gear types.

We deployed pop-off satellite archival tags (PSATs) on 14 olive ridley turtles Lepi- dochelys olivacea and 1 green turtle Chelonia mydas in the eastern tropical Pacific Ocean between November 2001 and June 2003 to determine dive behavior and post-release mortality following inter- actions with longline fishing gear. Nine olive ridleys and 1 green turtle were captured by longline fishing gear, and 5 free swimming olive ridleys were hand-captured at the surface to serve as con- trols. Hooks were removed from all longline-caught turtles, with the exception of 1 olive ridley turtle. PSATs remained on control- and longline-caught olive ridleys for an average of 61 and 54 d, respec- tively (range: 26 to 115) and on the green turtle for 26 d. Olive ridleys spent nearly all of their recorded time within the top 60 m, with very few dives exceeding 100 m. Over 95% of the time was spent between water temperatures of 22 and 28°C and turtles' dive behaviors appeared to be corre- lated with oceanographic variables (e.g. sea surface temperature and chlorophyll concentration). There were no clear differences evident either in horizontal movements, depth distributions, or asso- ciations with specific water temperatures between longline-caught and control turtles. Our data showed only one mortality event, that of a control turtle that died and sank 66 d after being tagged. We conclude that olive ridley turtles that are lightly hooked and handled properly survive and generally behave normally following interactions with shallow-set longline gear.

Sharks, turtles, billfish, and marine mammals are frequently caught accidentally in commercial fisheries. Although conservationists and fisheries managers encourage the release of these nontarget species, the long-term outcome of released animals is uncertain. Using blue sharks Prionace glauca, we developed a model to predict the long-term survival of released animals based on analysis of small blood samples. About 5% of the sharks were landed in obviously poor condition (lethargic and unresponsive to handling); these moribund sharks were sampled and euthanized. A subset of the remaining sharks was sampled and tagged with pop-up satellite archival tags (PSATs). Each of the PSATs that reported data (11 tags) showed that the sharks roamed at sea for at least 3 weeks postrelease. Five variables differentiated moribund sharks from survivors: Plasma Mg2+ (moribund, 1.57 ± 0.08 mM; survivor, 0.98 ± 0.05 mM; P < 0.00001), plasma lactate (moribund, 27.7 ± 4.1 mM; survivor, 5.80 ± 2.96 mM; P < 0.001), ery...

An approach to integrate sea surface temperature (SST) measurements into estimates of geolocations calculated by changes in ambient light level from data downloaded from pop-up satellite archival tags (PSAT) is presented. The model is an extension of an approach based on Kalman filter estimation in a statespace model. The approach uses longitude and latitude estimated from light, and SST. The extra information on SST is included in a consistent manner within the milieu of the Kalman filter. The technique was evaluated by attaching PSATs directly on thermistorequipped global positioning system drifter buoys. SSTs measured in the PSATs and drifter buoy were statistically compared with SSTs determined from satellites. The method is applied to two tracks derived from PSAT-tagged blue sharks (Prionace glauca) in the central Pacific Ocean. The inclusion of SST in the model produced substantially more probable tracks with lower prediction variance than those estimated from light-level data alone.

Temperature-depth recorders (TDRs) were attached to pelagic longline gear in the Hawaii-based commercial fishery to obtain actual fishing depths and to test the accuracy of catenary algorithms for predicting fishing depths. Swordfish gear was set shallow by typically deploying four hooks between successive floats. The observed depth of the settled deepest hook had a median value of 60 m for 333 swordfish sets. Tuna longline gear deployed more hooks between floats (mean = 26.8), and the observed median depth of the deepest hook was 248 m (n = 266 sets). Maximum gear depth was predicted from estimates of the longline sag ratio and catenary algorithms; however, depth was not predicted for all TDR-monitored sets because estimating sag ratios proved problematic. Swordfish sets had less slack in the main line and correspondingly smaller catenary angles (median = 54.2 ◦ ) than tuna sets (median = 63.7 ◦ ). Median values of the predicted catenary depth were 123 m for swordfish sets ( n = 203) and 307 m for tuna sets (n = 198). Shallow swordfish sets reached only ∼50% of their predicted depth, while deeper tuna sets reached about 70%. These values indicated that capture depths using traditional catenary equations may be biased without the benefit of TDRs affixed to longlines. Generalized linear models (GLMs) and generalized additive models (GAMs) were developed to explain the percentage of longline shoaling as a function of predicted catenary depth and environmental effects of wind stress, surface current velocity, and current shear. The GAM explained 67.2% of the deviance in shoaling for tuna sets and 41.3% for swordfish sets. Predicted catenary depth was always the initial variable included in the stepwise process, and the inclusion of environmental information in the GAM approach explained an additional 10–17% of the deviance compared to the GLMs. The explanatory ability of the environmental data may have been limited by the scale of the observations (1 ◦ in space; weekly or monthly in time) or the geometric (transverse versus in-line) forcing between the environment and longline set. Longline gear models with environmental forcing affecting shoaling may be improved in future studies by incorporating contemporaneous environmental information, although this may restrict analyses to fine-scale experimental longlines. Published by Elsevier B.V.

Quatro exemplares de agulhão-vela foram marcados com marcas eletrônicas monitoradas por satélite ('Pop-up satellite archival tags - PSATs') nas águas costeiras do Rio de Janeiro, sudeste do Brasil, durante janeiro e fevereiro de 2009 (agulhão-vela I e II) e entre novembro de 2010 e janeiro de 2011 (agulhão-vela III e IV). O número total de dias monitorados (ou seja, o tempo que as marcas permaneceram implantadas nos peixes) foram 12 (agulhão-vela I), 51 (agulhão-vela II), 16 (agulhão-vela III) e 43 dias (agulhão-vela IV). Os resultados demonstram um padrão claro de utilização do hábitat com a maior parte do tempo despendido predominantemente próximo à superfície do mar ocupando águas com uma faixa de temperatura restrita. Apesar da preferência por águas superficiais, os agulhões frequentemente realizaram mergulhos para águas mais profundas (ca. > 50 m) em intervalos de três a seis horas. A rota mais provável estimada a partir dos dados brutos de geolocalização e o modelo 'State-Space Kalman Filter' sugerem que os agulhões marcados não realizaram migrações significativas a partir do local de marcação. Em resumo, nossos resultados apresentam informações sobre a biologia da espécie no Atlântico Sudoeste e como as migrações verticais durante o dia e a noite são influenciadas pela temperatura da água e como essa informação pode auxiliar as avaliações de estoques de agulhão-vela no sudoeste do Atlântico. Pop-up satellite archival tags (PSATs) were deployed on four sailfish, Istiophorus platypterus, in the coastal waters of Rio de Janeiro State in southeast Brazil during January and February of 2009 (sailfish I and II) and between November 2010 and January 2011 (sailfish III and IV). The total number of days monitored (i.e., time that the tags remained attached) were 12 (sailfish I), 51 (sailfish II), 16 (sailfish III) and 43 days (sailfish IV). The results indicate a clear pattern of vertical habitat utilization with the majority of the time spent concentrated near the uniform sea surface layer occupying a relatively narrow temperature range. Despite the clear preference for epipelagic surface waters, sailfish regularly undertook vertical excursions into deeper waters (>50 m) within three to six hour intervals. Most Probable Tracks (estimated from raw geolocations using the state-space Kalman filter model) and linear displacements suggested that tagged sailfish did not move significant distances from the tagging site. In brief, our report provides information regarding the biology of sailfish in the southwestern Atlantic and how vertical distributions during the day and night are influenced by water temperature and how this information can improve sailfish stock assessments in southwestern Atlantic Ocean. Universidade Federal de São Paulo (UNIFESP) Departamento de Ciências do Mar University of Florida School of Forest Resources and Conservation Pelagic Research Group Instituto de Pesca Universidade Federal Rural de Pernambuco Departamento de Pesca e Aquicultura UNIFESP, Depto. de Ciências do Mar SciELO

Increasing fishing pressure on sharks stocks over recent decades has resulted in declines of many populations and led to increasing concerns for their conservation. The extent of these declines, however, has been highly variable—the result of the level of fishing, ocean conditions, and the life history of individual species. Two recent articles have described the collapse and possible extirpation of shark populations in the northwest Atlantic Ocean and Gulf of Mexico. Herein, we examine the results of these two papers commenting on the data sets used, comparing them to other available data sets, and critically evaluating the analyses and conclusions. We argue that these conclusions have been overstated because: (1) the analyses were based on a limited number of data sets, (2) the data sets themselves are inadequate to describe the status of all shark populations in the northwest Atlantic Ocean and Gulf of Mexico reported in these studies, (3) available data sets that could produce different concl...

The study of the early life history of large, open-ocean pelagic fishes such as tunas and billfish, and the identification of spawning and nursery habitats, has been extremely difficult as these animals are intrinsically rare, highly migratory, and difficult to study in captivity. Traditional methods such as the assembling of a developmental series of life stages, or the culturing of unknown eggs and larvae to a point where they can be identified, has not been easy or fruitful for many pelagic species. The discovery of a putative spawning 'hot spot' off the Kona coast of Hawaii, coupled with the devel- opment of shipboard approaches to real time identification and adaptive sampling of eggs, may pro- vide new approaches and insights into the spawning ecology and reproductive biology of these highly valuable but poorly known species. Here we report the use of a shipboard PCR based assay to differentiate species of istiophorid billfish larvae and identify eggs of istiophorid and xiphiid billfish, coryphaenid dolphinfish, and wahoo. A species-specific multiplex PCR assay was designed to amplify a single, unique size fragment of the mitochondrial cytochrome b gene for all 6 species of Indo-Pacific billfish, both dolphinfish, and the monospecific wahoo. A boiling technique used to extract DNA from larval eye tissue or an individual egg, combined with a single-step PCR assay and agarose electrophoresis, allowed species identification within 3 h of sample acquisition. This nearly real-time identification method for morphologically indistinguishable eggs and larvae provides an opportunity to employ adaptive sampling methods to increase sampling efficiency and will help in determining the spatial and temporal dimensions of spawning and nursery habitats offshore. This study describes the occurrence of blue marlin, dolphinfish, shortbill spearfish, swordfish and wahoo off the Kona coast by molecular approaches, and it provides the first description of the eggs of blue marlin, shortbill spearfish and wahoo.

Geolocation data were recovered from archival tags applied to bigeye tuna near Hawaii. A state-space Kalman filter statistical model was used to estimate geolocation errors, movement parameters, and most probable tracks from the recovered data. Standard deviation estimates ranged from 0.5� to 4.4� latitude and from 0.2� to 1.6� longitude. Bias estimates ranged from )1.9� to 4.1� latitude and from )0.5� to 3.0� longitude. Estimates of directed movement were close to zero for most fish reaching a maximum magnitude of 5.3 nm day )1 for the one fish that moved away from its release site. Diffusivity estimates were also low, ranging from near zero to 1000 nm 2 day )1 . Low values of the estimated movement parameters are consistent with the restricted scale of the observed movement and the apparent fidelity of bigeye to geographical points of attraction. Inclusion of a time-dependent model of the variance in geolocation estimates reduced the variability of latitude estimates. The statespace Kalman filter model appears to provide realistic estimates of in situ geolocation errors and movement parameters, provides a means to avoid indeterminate latitude estimates during equinoxes, and is a potential bridge between analyses of individual and population movements.

To learn more about the movement patterns of bigeye tuna (Thunnus obesus), we deployed archival tags on 87 fish ranging in fork length from 50 to 154 cm. Thirteen fish were recaptured, from which 11 archival tags were returned, representing in aggregate 943 days-at-liberty. We successfully retrieved data from 10 tags, representing 474 days in aggregate. The largest fish recaptured was 44.5 kg [131 cm fork length (FL)] and the smallest 2.8 kg (52 cm). The deepest descent recorded was 817 m, the coldest temperature visited 4.7� C, and minimum oxygen level reached � 1m L L )1 . Fish spent little time at depths where water temperatures were below 7� C and oxygen levels less than � 2m L L )1 . Five fish were recaptured near the offshore weather buoy where they were tagged. Based on vertical movement patterns, it appeared that all stayed immediately associated with the buoy for up to 34 days. During this time they remained primarily in the uniform temperature surface layer (i.e. above 100 m). In contrast, fish not associated with a floating object showed the W-shaped vertical movement patterns during the day characteristic of bigeye tuna (i.e. descending to � 300‐500 m and then returning regularly to the surface layer). Four fish were tagged and subsequently recaptured near Cross Seamount up to 76 days later. These fish exhibited vertical movement patterns similar to, but less regular than, those of fish not associated with any structure. Bigeye tuna appear to follow the diel vertical movements of the deep sound scattering layer (SSL) organisms and thus to exploit them effectively as a prey resource. Average night-time depth was correlated with lunar illumination, a behaviour which mimics movements of the SSL.

Campana et al. (2009; Mar Ecol Prog Ser 387:241-253) explored the survival of blue sharks Prionace glauca captured and released from the North Atlantic commercial longline fishery. We think that their comments and comparisons do not accurately reflect a previous survival study of blue sharks in Hawaii (Moyes et al. 2006; Trans Am Fish Soc 135:1389-1397). The differences in mor- tality between the studies, ~5% in the Hawaii-based fishery and ~35% in the North Atlantic fishery, were suggested to be due to failure of Moyes et al. (2006) to accurately reflect commercial fishing conditions. Careful examination of the data, however, suggests that the mortality depends on fishery- specific features — hook type, soak time and handling of the bycatch during release — rather than the respective tagging protocols. Survival studies based on pop-up satellite archival tags (PSATs) are cost-prohibitive; alternative (e.g. biochemical) approaches to estimate stress and morbidity are needed to supplant PSAT studies and to increase sample sizes. Standardization of fishing methods and sampling protocol is needed for future survival studies, to reduce experimental bias and improve the cost:benefit relationship.

Post-release behaviour modification, possibly a result of capture and handling stress, was evaluated using empirical eigenfunction analysis to detect changes in vertical movement patterns recorded by 183 pop-up satellite archival tags (PSATs) deployed on large pelagic fish. Argos-transmitted summary, timed interval, and some archival data were included. Scoring of irregular post-release behaviour was based on a separation of plotted eigenfunction coefficient values by their mean, with the transection across the mean reference line denoting the duration of irregular behaviour. In all, 67 (36.6%) individual fish exhibited irregular behaviour, lasting from 3 to 60 d (mean = 15.8, s.d. = 10.4). An additional 27 (14.8%) displayed patterns suggestive of irregular behaviour. Data quality and quantity were important criteria for revealing behaviour patterns. Irregular behaviour was detected in 32.6% of Argos-transmitted dataseries, increasing to 60.6% in the higher-resolution archival series. Decreased vertical movement characterized the irregular behaviour of blue sharks (Prionace glauca) and porbeagles (Lamna nasus), whereas all other species showed increased vertical activity. The approach described provides a useful method of revealing behavioural modification during the post-release recovery period of PSAT-tagged large pelagic fish, although the extent of influence on normal behaviour is not fully understood., Sí

An optimal search theory, the so-called Levy-flight foraging hypothesis1, predicts that predators should adopt search strategies known as Levy flights where prey is sparse and distributed unpredictably, but that Brownian movement is sufficiently efficient for locating abundant prey2, 3, 4. Empirical studies have generated controversy because the accuracy of statistical methods that have been used to identify Levy behaviour has recently been questioned5, 6. Consequently, whether foragers exhibit Levy flights in the wild remains unclear. Crucially, moreover, it has not been tested whether observed movement patterns across natural landscapes having different expected resource distributions conform to the theory’s central predictions. Here we use maximum-likelihood methods to test for Levy patterns in relation to environmental gradients in the largest animal movement data set assembled for this purpose. Strong support was found for Levy search patterns across 14 species of open-ocean predatory fish (sharks, tuna, billfish and ocean sunfish), with some individuals switching between Levy and Brownian movement as they traversed different habitat types. We tested the spatial occurrence of these two principal patterns and found Levy behaviour to be associated with less productive waters (sparser prey) and Brownian movements to be associated with productive shelf or convergence-front habitats (abundant prey). These results are consistent with the Levy-flight foraging hypothesis1, 7, supporting the contention8, 9 that organism search strategies naturally evolved in such a way that they exploit optimal Levy patterns.

Latitude estimates from light recorded by electronic data storage tags typically contain large errors, particularly at times near the equinoxes. We employ error propagation analysis to the fundamental equation relating latitude to solar elevation and time of day. Large latitude errors are caused by mathematical “amplification” of small errors in relating solar irradiance to solar elevation. Furthermore, the sign of these errors is such that the estimated latitude is badly biased. This analysis leads directly to a method of removing systematic error (bias) from latitude estimates in state-space track reconstruction models. Preliminary implementation of this method effectively removes all bias from latitude estimated from solar irradiance recorded by archival tags deployed both on moorings and on freely swimming tuna.

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability1. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology1, 2, 3. Lévy walks4 are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes5. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested6, 7. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators—sharks, bony fishes, sea turtles and penguins—exhibit Lévy-walk-like behaviour close to a theoretical optimum2. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms3, from microbes8 to humans9, as a 'rule' that evolved in response to patchy resource distributions.

We analyzed water temperature, visceral cavity temperature and depth data from archival tags retrieved from bigeye tuna (Thunnus obesus) at liberty in the central Pacific for up to 57 days using a mathematical model of heat exchange. Our model took into account the transfer of heat between the portions of the myotomes comprising red muscle fibers adjacent to the spinal column and served by vascular counter current heat exchanges (henceforth referred to as ;red muscle') and the water, as well as between the red muscle and the temperature sensor of the archival tags in the visceral cavity. Our model successfully predicted the recorded visceral cavity temperatures during vertical excursions provided that the rate constants for heat transfer between the ambient water and the red muscle during cooling (k(low)) and those during heating (k(high)) were very dissimilar. Least-squares fitting of k(low) and k(high) for the entire period that the fish were at liberty yielded values generally in the ranges 0.02-0.04 min(-1) and 0.2-0.6 min(-1) (respectively), with an average ratio k(high)/k(low) of approximately 12. Our results confirmed those from previous studies showing that bigeye tuna have extensive physiological thermoregulatory abilities probably exerted through changes of blood flow patterns that controlled the efficiency of vascular countercurrent heat exchanges. There was a small but significant negative correlation between k(low) and size, whereas there was no correlation between k(high) and size. The maximum swimming speeds during vertical excursions (calculated from the pressure data) occurred midway during ascents and averaged approximately 2 FL s(-1) (where FL=fork length), although speeds as high approximately 4-7 FL s(-1) were also noted.

Large pelagic fishes (tuna, billfish, and sharks) are being tagged with ‘pop-up’ satellite archive electronic sensors (PSAT), which measure and log detailed data on the swimming environment of the fish, as well as light data, which are used to estimate the geographic locations of the fish. At predetermined periods the sensors are programmed to ‘pop-off’ the fish, float to the sea surface, and transmit the data collected to Argos satellites, which relay the data to ground stations on earth. Processing of these data provides detailed time-history information on the environment and estimated locations of individual free-swimming fish. The resulting information is then examined in conjunction with ocean measurements and data products derived from various satellite ocean sensors including sea surface temperature, ocean color, and ocean winds, as well as SODA ocean data assimilation model analyses. The fish habitats are thus defined in the context of surrounding ocean conditions, measured contemporaneously by oceanic satellite remote sensing and derived from outputs from the SODA ocean simulation model. An important aspect of this approach is that it provides the opportunity to identify, and subsequently monitor with satellite remote sensing, ocean features, processes, and properties that may play important roles in determining spatial and temporal variations in marine fish habitats. Data are presented that demonstrate this approach for blue shark, Prionace glauca.

We tested the ability of archival tags and their associated algorithms to estimate geographical position based on ambient light intensity by attaching six tags (three tags each from Northwest Marine Technologies [NMT] and Wildlife Computers [WC]) at different depths to a stationary mooring line in the Pacific Ocean (approx. 166°42′W, 24°00′N), for approximately one year (29-Aug-98 to 16-Aug-99). Upon retrieval, one tag each from the two vendors had malfunctioned: from these no data (NMT) or only partial data (WC) could be downloaded. An algorithm onboard the NMT tag automatically calculated geographical positions. For the WC tags, three different algorithms were used to estimate geographical positions from the recorded light intensity data. Estimates of longitude from all tags were significantly less variable than those for latitude. The mean absolute error for longitude estimates from the NMT tags ranged from 0.29 to 0.35°, and for the WC tags from 0.13 to 0.25°. The mean absolute error in latitude estimates from the NMT tags ranged from 1.5 to 5.5°, and for the WC tags from 0.78 to 3.50°. Ambient weather conditions and water clarity will obviously introduce errors into any geoposition algorithm based on light intensity. We show that by applying objective criteria to light level data, outliers can be removed and the variability of geographical position estimates reduced. We conclude that, although archival tags are suitable for questions of ocean basin-scale movements, they are not well suited for studies of daily fine scale movement patterns because of the likely magnitude of position estimate errors. For studies of fine scale movements in relation to specific oceanographic conditions, forage densities and distance scales of 100 km or less, other methods (e.g. acoustic tracking) remain the tool of choice.

Allopatric populations of Australian freshwater eel-tailed catfish, Tandanus tandanus, were compared morphologically and electrophoretically. Five populations from east of the Great Dividing Range and six from within the MurrayDarling basin, west of the Great Dividing Range, were sampled. An absence of morphological differentiation among all populations was in contrast to electrophoretic evidence in which fixed allelic differences revealed three discrete gene pools: (1) an undescribed species from the Bellinger River; (2) a second undescribed species from the Nymboida River; and (3) the remaining populations that were genetically similar to one another. Mean heterozygosity in all populations ranged from 0.000-0.011.