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Purse-seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade-offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high-risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse-seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1° × 1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1-11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10-19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21-41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO., (© 2024 The Authors. Conservation Biology published by Wiley Periodicals LLC on behalf of Society for Conservation Biology.)

The sea surface temperature and surface currents during 1993–2016 based on satellite remote sensing, along with the ocean temperature and currents during 1993–2013 from a data assimilative ocean simulation product, are analyzed to investigate the influence of the Galápagos Islands (GI) in the eastern tropical Pacific on the sea surface temperature. Variations of the cold core west of the GI are quantified by TC − TW, TC − TE, and the cold core area (CCA), where TW, TC, and TE are the sea surface temperature to the west of the cold core, in the cold core, and to the east of the GI, respectively. TC − TE and the CCA show a stronger influence of the GI in boreal fall than in spring, in contrast to TC − TW, which shows a stronger influence in spring than in fall. All three indices show weaker (stronger) GI's influence during El Niño (La Niña) years, but only CCA and TC − TE have significant correlations of −0.66 and 0.61 with the Niño3 index. Variations of TC − TW are related to that of upwelling immediately the west of the GI. Variations of TC − TE and CCA are related to that of the spatial distributions of the upper ocean temperature, the advection of temperature by the horizontal currents, specifically the north branch of the South Equatorial Current, and upwelling in the eastern tropical Pacific. Key Points: Two new indices are defined to quantify the influence of Galápagos Islands on SST in Eastern Tropic PacificNew indices show stronger (weaker) Islands' influence in boreal fall (spring) and during La Niña (El Niño) yearsVariations of the Islands' influence are related to distributions of background temperature, upwelling, and surface currents [ABSTRACT FROM AUTHOR]

The failure to achieve fisheries management objectives has been broadly discussed in international meetings. Measuring the effects of fishery regulations is difficult due to the lack of detailed information. The yellowfin tuna fishery in the eastern Pacific Ocean offers an opportunity to evaluate the fishers' responses to temporal regulations. We used data from observers on-board Mexican purse-seine fleet, which is the main fleet fishing on dolphin-associated tuna schools. In 2002, the Inter-American Tropical Tuna Commission implemented a closed season to reduce fishing effort for this fishery. For the period 1992-2008, we analysed three fishery indicators using generalized estimating equations to evaluate the fishers' response to the closure. We found that purse-seiners decreased their time spent in port, increased their fishing sets, and maintained their proportion of successful fishing sets. Our results highlight the relevance of accounting for the fisher behaviour to understand fisheries dynamics when establishing management regulations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modeled mercury transport in eastern tropical and central north Pacific food webs. [•] Tuna mercury concentrations increased by factors of two to four in the ETP model. [•] Differences in tuna mercury can be explained by the diets of tuna and their prey. [•] Mercury at the base of the food web influences concentrations in top predators. [•] Predicted regional differences in tuna mercury reflect empirical observations. [Copyright &y& Elsevier]

Abstract: A critical need exists for quantitative reconstructions of long-term El Niño Southern Oscillation (ENSO) variability in the eastern tropical Pacific. Presented here is a method to quantitatively estimate past changes 1) in the seasonal amplitude of sea surface temperature (SST) in the Peruvian coastal upwelling system and 2) in the amplitude of ENSO-related interannual variability in the eastern tropical Pacific. The seasonal amplitude of SST (ΔT) along the length of the Peruvian coast is strongly correlated with the Niño1+2 index. We show that the frequency distribution of ΔT values provided by a modern sample of 13 Mesodesma donacium shells faithfully reflects modern ENSO variability at the regional scale, including the range of anomalies from La Niña to moderate El Niño events, but excludes extreme warm anomalies because of high shell mortality. We propose to use the frequency distribution of ENSO anomalies in paleoclimate studies for comparisons between shell records, coral records, and GCM simulations. Reconstruction uncertainties can be quantified using Monte Carlo simulations. The method presented here opens new perspectives for quantitative paleo-ENSO reconstructions in the Eastern Pacific since it may be applied with any mollusk species from Peru provided at least one annual cycle of SST is faithfully recorded by shell δ18O. [Copyright &y& Elsevier]

Our present knowledge of marine macroalgal diversity for the Central American Pacific coast is limited by the short history of investigations (ca. 100 years) and few algal specialists through a large geographical area. While recent checklists have emerged for other regions of the eastern Pacific, there have been virtually no attempts to inventory macroalgal diversity for the Pacific of Central America. This checklist of the marine macroalgae was developed based on published scientific literature and unpublished records in student theses. A total of 379 species records are regarded as current valid names of marine macroalgae. The red algae (Rhodophyta) had the highest species number (252 species), followed by green algae (Chlorophyta: 81 species) and brown algae (Phaeophyceae: 46 species). The country with the greatest diversity of marine macroalgae is Costa Rica with 216 species, followed by Panama with 174, El Salvador with 146, Nicaragua with 24, and Guatemala with 16. At present, there are no published records for the Pacific coast of Honduras. Variation in number of species throughout the Pacific coast of Central America is likely due to differences in geomorphology, habitat heterogeneity among national coastal-marine zones, and unbalanced research efforts. [ABSTRACT FROM AUTHOR]

Abstract: Within the eastern tropical oceans of the Atlantic and Pacific basin vast oxygen minimum zones (OMZ) exist in the depth range between 100 and 900m. Minimum oxygen values are reached at 300–500m depth which in the eastern Pacific become suboxic (dissolved oxygen content <4.5μmolkg−1) with dissolved oxygen concentration of less than 1μmolkg−1. The OMZ of the eastern Atlantic is not suboxic and has relatively high oxygen minimum values of about 17μmolkg−1 in the South Atlantic and more than 40μmolkg−1 in the North Atlantic. About 20 (40%) of the North Pacific volume is occupied by an OMZ when using 45μmolkg−1 (or 90μmolkg−1, respectively) as an upper bound for OMZ oxygen concentration for ocean densities lighter than σ θ <27.2kgm−3. The relative volumes reduce to less than half for the South Pacific (7% and 13%, respectively). The abundance of OMZs are considerably smaller (1% and 7%) for the South Atlantic and only ∼0% and 5% for the North Atlantic. Thermal domes characterized by upward displacements of isotherms located in the northeastern Pacific and Atlantic and in the southeastern Atlantic are co-located with the centres of the OMZs. They seem not to be directly involved in the generation of the OMZs. OMZs are a consequence of a combination of weak ocean ventilation, which supplies oxygen, and respiration, which consumes oxygen. Oxygen consumption can be approximated by the apparent oxygen utilization (AOU). However, AOU scaled with an appropriate consumption rate (aOUR) gives a time, the oxygen age. Here we derive oxygen ages using climatological AOU data and an empirical estimate of aOUR. Averaging oxygen ages for main thermocline isopycnals of the Atlantic and Pacific Ocean exhibit an exponential increase with density without an obvious signature of the OMZs. Oxygen supply originates from a surface outcrop area and can also be approximated by the turn-over time, the ratio of ocean volume to ventilating flux. The turn-over time corresponds well to the average oxygen ages for the well ventilated waters. However, in the density ranges of the suboxic OMZs the turn-over time substantially increases. This indicates that reduced ventilation in the outcrop is directly related to the existence of suboxic OMZs, but they are not obviously related to enhanced consumption indicated by the oxygen ages. The turn-over time suggests that the lower thermocline of the North Atlantic would be suboxic but at present this is compensated by the import of water from the well ventilated South Atlantic. The turn-over time approach itself is independent of details of ocean transport pathways. Instead the geographical location of the OMZ is to first order determined by: (i) the patterns of upwelling, either through Ekman or equatorial divergence, (ii) the regions of general sluggish horizontal transport at the eastern boundaries, and (iii) to a lesser extent to regions with high productivity as indicated through ocean colour data. [Copyright &y& Elsevier]

Factors affecting mesozooplankton distributions in the northeastern tropical Pacific Ocean were investigated using data obtained along a meridian line (5°–12°N, 131.5°W) in the summers of 1998, 1999, and 2003. The survey periods corresponded to a sharp transition between the 1997–1998 El Niño and 1998–1999 La Niña events, the 1999 La Niña event, and near-normal conditions after the moderate 2002–2003 El Niño in the equatorial Pacific. A strong upwelling in the divergence zone from 10.5° to 11°N caused a shoaling of the thermocline depth (∼30m), resulting in increases in nitrate and phytoplankton chlorophyll a (chl-a) concentrations, and, in turn, mesozooplankton abundance during the La Niña in 1999. In contrast, in 1998, remnants of El Niño characteristics, deeper thermocline depth (60–150m) and warm surface water (>28°C), led to low concentrations of nitrate, chl-a and low mesozooplankton abundance, except in the convergence zone around 7°N. The thermocline depth and nitrate concentration obtained during the near-normal period in 2003 corresponded to intermediate values as compared to those obtained during El Niño and La Niña conditions. Interannual changes in the position and strength of ecotones, such as divergence and convergence zones, affected mesozooplankton community structure and cyclopoid-to-calanoid ratios along the 131.5°W meridian line. The clustering pattern of the mesozooplankton community was mostly characterized by calanoid (mainly Clausocalanus sp.) and cyclopoid (mainly Oncaea sp.) copepods, accounting for most of the observed differences among groups during the study period. Cyclopoids and calanoids were more abundant in 1999 than in 1998 or 2003, with a sharp increase to the north, while they were less abundant to the north in 1998 and 2003. The cyclopoid-to-calanoid ratio peaked in the convergence zone in 1998 and the divergence zones in 1999 and 2003, apparently due to the strength and location of the ecotones. Principal component analysis (PCA) with environmental factors and dominant mesozooplankton groups showed that dominant groups were affected by nitrate and chl-a concentrations in 1998, by sigma-t (water density), nitrate and chl-a concentrations in 1999, and by sigma-t, salinity and chl-a concentration (except siphonophores) in 2003. Latitudinal distribution of thermocline depth before and after the 1998/99 La Niña event showed a distinct interannual difference. The abundance of mesozooplankton in the divergence zone in 1999 was distinctively higher than abundances found in the convergence and divergence zones in 1998 and 2003, which resulted from the shallow thermocline depth due to an intensified upwelling during the strong 1998–1999 La Niña event. [Copyright &y& Elsevier]

Fishing pressure has increased the extinction risk of many elasmobranch (shark and ray) species. Although many countries have established no-take marine reserves, a paucity of monitoring data means it is still unclear if reserves are effectively protecting these species. We examined data collected by a small group of divers over the past 21 years at one of the world's oldest marine protected areas (MPAs), Cocos Island National Park, Costa Rica. We used mixed effects models to determine trends in relative abundance, or probability of occurrence, of 12 monitored elasmobranch species while accounting for variation among observers and from abiotic factors. Eight of 12 species declined significantly over the past 2 decades. We documented decreases in relative abundance for 6 species, including the iconic scalloped hammerhead shark (Sphyrna lewini) (-45%), whitetip reef shark (Triaenodon obesus) (-77%), mobula ray (Mobula spp.) (-78%), and manta ray (Manta birostris) (-89%), and decreases in the probability of occurrence for 2 other species. Several of these species have small home ranges and should be better protected by an MPA, which underscores the notion that declines of marine megafauna will continue unabated in MPAs unless there is adequate enforcement effort to control fishing. In addition, probability of occurrence at Cocos Island of tiger (Galeocerdo cuvier), Galapagos (Carcharhinus galapagensis), blacktip (Carcharhinus limbatus), and whale (Rhincodon typus) sharks increased significantly. The effectiveness of MPAs cannot be evaluated by examining single species because population responses can vary depending on life history traits and vulnerability to fishing pressure., (© 2015 Society for Conservation Biology.)