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Several commercially and ecologically important species in the southern Benguela have undergone southward and eastward shifts in their distributions over previous decades, most notably the small pelagic fish sardine Sardinops sagax and anchovy Engraulis encrasicolus. Understanding these changes and their implications is essential in implementing an ecosystem approach to fisheries in the southern Benguela and attempting to appreciate the potential impacts of future environmental change. To investigate possible impacts of these shifts at an ecosystem level, distribution maps for before (1985–1991), during (1997–2000) and after (2003–2008) the shift in small pelagic fish were constructed for 14 key species from catch and survey data, and used to calculate spatial indicators including proportion east and west of Cape Agulhas, relative overlap in biomass and area, index of diversity, connectivity. Potential interactions on the south and west coasts were also compared. For several species (redeye; chub mackerel; kingklip; chokka squid; yellowtail), previously unidentified increases in the proportion of biomass east of Cape Agulhas were shown to have occurred over the same period as that of small pelagic fish, although none to the same degree. On average, overlap with small pelagic fish increased over time and overall system connectivity was lowest in the intermediate period, possibly indicating a system under transition. Connectivity declined over time on the west coast while increasing on the east coast. Distributions of other species have changed over time, with the region east of Cape Agulhas becoming increasingly important in terms of potential trophic interaction. Variations in distribution of biomass and structural complexity affect the trophic structure and hence functioning of the system, and implications should be considered when attempting to identify the possible ecosystem impacts of current and future system-level change. [ABSTRACT FROM AUTHOR]

Demer, D. A., and Zwolinski, J. P. 2014. Corroboration and refinement of a method for differentiating landings from two stocks of Pacific sardine (Sardinops sagax) in the California Current. – ICES Journal of Marine Science, 71: 328–335.Efforts to survey, assess and manage Pacific sardine (Sardinops sagax) in the California Current may depend on accurate differentiation of the purported two migrating stocks. The southern stock spans seasonally from southern Baja California, México to Point Conception, California; the northern stock spans seasonally from Punta Eugenia, México northwards to southern Alaska. Their seasonal north–south migrations are approximately synchronous within their respective domains, resulting in segregated spawning and different identities. A decade ago, a practical method was proposed for differentiating landings from the two stocks using concomitant measurements of sea-surface temperature (SST). Here, we corroborate and refine the method using regional indices of optimal and good potential habitat for the northern stock, and SST-based indices associated with the 99.9 and 100% confidence intervals of the potential habitat. For months when the index is <0.5, (i.e. when the minority of a fishing region probably includes potential northern stock habitat), the landings are attributed to the southern stock, and vice versa. We applied this method to regional monthly landings data from 2006–2011 and the results indicated that an average of 63–72 and 32–36% of the summertime landings at Ensenada, México and San Pedro, southern California were probably from the southern stock, respectively, depending on the index used. Allocation error could be reduced if the landings were evaluated on finer spatio-temporal scales, particularly during habitat-transition periods. Our method may be used to improve estimates of northern stock biomass, spatial and length distributions, recruitment, and mortality. [ABSTRACT FROM PUBLISHER]

Demer, D. A., Zwolinski, J. P., Cutter, G. R. Jr, Byers, K. A., Macewicz, B. J., and Hill, K. T. Sampling selectivity in acoustic-trawl surveys of Pacific sardine (Sardinops sagax) biomass and length distribution. – ICES Journal of Marine Science, 70: .To annually assess the northern stock of Pacific sardine (Sardinops sagax) in the California Current and set harvest quotas for the US fishery, managers have used an age-structured stock synthesis model fitted with results from acoustic-trawl (ATM), daily-egg-production, and aerial-photogrammetric survey methods, fishery landing and individual-length data, and many assumed or empirically derived parameters. In these assessments, sardine landed at ports spanning from Ensenada, México to Vancouver Island, Canada were assumed to be solely from the northern stock. It was also assumed that the ATM estimates of sardine biomass were negligibly biased for the sizes of fish sampled by the survey trawls (i.e., catchability q = 1 for sardine standard length (SL) values greater than ∼17 cm). Due to these catchability and length-selectivity assumptions, the ATM- and assessment-estimated abundances are mostly similar for larger sardine. However, the assessment estimates include large abundances of small sardine (SL values less than ∼15 cm) that are not represented in either the ATM-survey results or the fishery landings, and generally did not recruit to the migrating northern stock sampled by the ATM surveys. We considered four explanations for this disparity: (i) the ATM length-selectivity assumption is correct; (ii) the non-recruiting small fish may comprise a smaller portion of the stock than indicated by the assessments; (iii) during years of low recruitment success, those size classes may be virtually completely fished by the Ensenada and San Pedro fisheries; or (iv) they may belong to the southern sardine stock. This investigation emphasizes the previously identified importance of differentiating samples from the northern and southern stocks and surveying their entire domains. [ABSTRACT FROM PUBLISHER]

The article focuses on comments of several researchers on temperature-dependent stock-recruit modeling for Pacific sardine. It states that spawner–recruit models with the dependent variables including log recruitment were estimated by L.D. Jacobson and A.D. MacCall. It informs that S. McClatchie and colleagues estimated a significant relationship between log recruitment and spawning biomass and M. Lindegren and D. M. Checkley examined the temperature effects on Pacific sardine recruitment.

Abstract: Asymmetry in transboundary fish stock distribution caused by climate variability can make the stability of cooperative management challenging. Pacific sardine (Sardinops sagax), which exhibits extreme decadal variability in abundance and geographic distribution corresponding to water temperature regime shifts within the California Current Ecosystem, is expected to face such issues. Pacific sardine is a transboundary resource targeted by Mexican, U.S. and Canadian fisheries. Our study applies a three-agent game theoretic model that incorporates environmental effects on Pacific sardine abundance and biomass distribution. Simulations are conducted to evaluate the stability of full and partial cooperative management of the Pacific sardine fishery, under seven different climate variability scenarios. Our results show that ocean climate variability could motivate the formation of stable cooperative management outcomes for the Pacific sardine fisheries operated by Canada, the U.S. and Mexico. [Copyright &y& Elsevier]

Analyses of data collected over a decade off southern Australia confirm that estimates of spawning biomass of Sardinops sagax obtained using the daily egg production method are imprecise and suggest that if inappropriate analytical methods are used, estimates may also be biased. Spawning biomass estimates are most affected by variation in mean daily egg production (P0), spawning area, and spawning fraction. The log-linear mortality model (with one egg added to each day class of eggs at each positive site) should be used to estimate P0 because it fits strongly over-dispersed sardine egg density data better and provides more logically consistent and precautionary estimates of P0 than the exponential mortality model or generalized linear models. Most generalized linear models produced inflated estimates of P0 when egg data were strongly over-dispersed. The area surveyed should be sub-divided into a large number (e.g., 300) of similar sized grids. The Voronoi natural neighbor method should be used to calculate grid size for estimation of the spawning area because it reduces subjectivity in sub-division of the sampling area. Potential biases in spawning fraction can be minimized by calculating this parameter using data from all three stages of post-ovulatory follicles (combined). Priorities for future research are identified. [ABSTRACT FROM AUTHOR]

Hurtado-Ferro, F., Hiramatsu, K., and Shirakihara, K. 2010. Allowing for environmental effects in a management strategy evaluation for Japanese sardine. – ICES Journal of Marine Science, 67: 2012–2017.The Japanese sardine (Sardinops melanostictus) is a valuable, but highly variable, resource. After record catches during the late 1980s, a 4-year recruitment failure, coupled with overfishing, resulted in severe stock depletion. TAC-based management was introduced in 1997, but the trend has not been reversed and the biomass is now 2 orders of magnitude below the value in 1987. Although a strong correlation exists between winter sea surface temperature (SST) in the nursery area and recruitment, uncertainty about future environmental effects is not explicitly considered in the management. We evaluate the robustness of three catch rules to environmental uncertainty, as captured by three stock–recruitment models (one without an environmental factor and two based on correlations between recruitment and SST for two datasets), in terms of the risk of further depletion, average biomass, and average catch: a constant fishing mortality (CF), a strategy that follows the Japanese guidelines (JG), and a more conservative strategy (ENV) that uses a temperature threshold as a proxy for regime shifts to switch between alternative catch rules. ENV and JG performed better than CF, with ENV displaying better performance in the long term, but differences were negligible in the short term. [ABSTRACT FROM PUBLISHER]

Abstract: This paper develops a simple bioeconomic model to investigate the economic and ecological issues associated with the commercial harvest of Pacific sardines relative to their value as forage for commercially, recreationally, and ecologically important predators in the California Current ecosystem. The model was used to evaluate how changes in the net per unit value of sardines, the net per unit value of sardine predators, and the transfer efficiency of predators affect the total net value of sardines, i.e. the net value of catches and the net value from sardine predation. Given recent market conditions for sardines and their commercial predators, and transfer efficiencies derived from predation data of the 1960s, it was found that the value of commercially caught predators and the efficiency by which they convert sardines to exploitable biomass were most important in determining the viability of the sardine fishery. The values assumed for predators that are not commercially caught were of no consequence under these conditions. Taking the value of sardines as forage into account does not necessarily mean an either-or situation for the fishery. As long as there is some measure of net value from the fishery and net value from predation, both benefit society at large. [Copyright &y& Elsevier]

Abstract: The Pacific sardine (Sardinops sagax) supports one of the most important fishing industries of the northeastern Pacific Ocean (NPO). The recruitment of juveniles in the NPO has shown fluctuations in recent decades; this has been attributed to variations in the spawning stock biomass (SSB) and to the oceanographic conditions within the California Current system (CCS). In this study, these hypotheses are tested by fitting three different stock–recruitment (SR) functions into different models using data of recruitment and SSB of Pacific sardine in three regions of the NPO: Magdalena Bay (MB), Ensenada (EN), and north Pacific (NP). To quantify the plausibility of each model, given the data and the set of three models, the Akaike weight of each model was calculated. The selection of the best model within each area was done by minimizing the small-sample, bias-corrected form of the Akaike information criterion. Through this approach, the MB and EN fisheries fitted both the asymptotic Beverton–Holt and dome-shaped Ricker models. These results agreed with prior evidence that recruitment of Pacific sardine has a density-dependent mortality term for eggs and juvenile stages, related to the total SSB and cohort size. To test environmental influence on sardine recruitment principal component analysis was undertaken. The first principal component group was determined by El Niño–La Niña episodes; the second, by the upwelling index. Upon incorporation of these principal components into the SR models, the recruitment of the sardine throughout the CCS was differentially affected, e.g., warm episodes in MB negatively affected recruitment, whereas in the EN and NP regions, the effect was positive. [Copyright &y& Elsevier]

Abstract: The Humboldt Current System, like all upwelling systems, has dramatic quantities of plankton-feeding fish, which suggested that their population dynamics may ‘drive’ or ‘control’ ecosystem dynamics. With this in mind we analysed the relationship between forage fish populations and their main prey, zooplankton populations. Our study combined a zooplankton sampling program (1961–2005) with simultaneous acoustic observations on fish from 40 pelagic surveys (1983–2005) conducted by the Peruvian Marine Research Institute (IMARPE) and landing statistics for anchoveta (Engraulis ringens) and sardine (Sardinops sagax) along the Peruvian coast from 1961 to 2005. The multi-year trend of anchoveta population abundance varied consistently with zooplankton biovolume trend, suggesting bottom-up control on anchovy at the population scale (since oceanographic conditions and phytoplankton production support the changes in zooplankton abundance). For a finer-scale analysis (km) we statistically modelled zooplankton biovolume as a function of geographical (latitude and distance from the 200-m isobath), environmental (sea surface temperature), temporal (year, month and time-of-day) and biological (acoustic anchovy and sardine biomass within 5km of each zooplankton sample) covariates over all survey using both classification and regression trees (CART) and generalized additive models (GAM). CART showed local anchoveta density to have the strongest effect on zooplankton biovolume, with significantly reduced levels of biovolume for higher neighbourhood anchoveta biomass. Additionally, zooplankton biovolume was higher offshore than on the shelf. GAM results corroborated the CART findings, also showing a clear diel effect on zooplankton biovolume, probably due to diel migration or daytime net avoidance. Apparently, the observed multi-year population scale bottom-up control is not inconsistent with local depletion of zooplankton when anchoveta are locally abundant, since the latter effect was observed over a wide range of overall anchoveta abundance. [Copyright &y& Elsevier]

The biomass of small pelagic fish species off the coast of South Africa has been monitored since 1984 using hydro-acoustic survey techniques. These time-series of spawner biomass and recruitment estimates form the basis for management of both the South African sardine Sardinops sagax and anchovy Engraulis encrasicolus resources and are central to the setting of annual total allowable catch levels. However, these survey estimates have, for the most part, been treated as relative indices as there are several biases inherent in acoustic survey methodology that remain difficult to quantify. Advances in acoustic technology together with an improved understanding of the major sources of survey errors have enabled estimation of and correction for biases such as receiver saturation, acoustic signal attenuation and target strength. Incorporation of these corrections over the entire time-series has resulted in an improved accuracy of acoustic survey estimates and substantial changes to the biomass estimates of both species, without jeopardising the requirement that the time-series remains comparable throughout its duration. Furthermore, the resultant decrease in the level of uncertainty associated with these abundance estimates has rendered improved utilisation of these resources possible. [ABSTRACT FROM AUTHOR]

Abstract An Empirical Biomass Model for the Japanese sardine, Sardinops melanostictus , was developed on the basis of the relationship between February sea surface temperature (SST) in the Kuroshio Extension (30–35°N, 145–180°E) and the mortality coefficient during the period from egg to age 1, observed in 1979–94, to examine the long-term variation of biomass. The periods of the good and bad catch, the year of the biomass peak, and the speed of the biomass decline in the period from 1957 to 1994 were successfully reproduced, except for the biomass increase in the early 1970s. When the model also included with a density-dependent effect, the whole history of the observed catch during 1957–94 was almost perfectly reproduced. These results suggest that the environment in the Kuroshio Extension region, represented by winter–spring SST, is regarded as a leading factor for determining fluctuations of the sardine biomass in the long term, and that the density effect has a secondary contribution. [ABSTRACT FROM AUTHOR]

Climate regime shifts in the Northeast Pacific appear to have forced population size changes associated with major geographical variations in the position of the center of distribution and bulk of biomass of Pacific sardine (Sardinops caeruleus). These findings help explain the disappearance of sardines around 60 years ago at the northern part of the California Current System and their return following the 1980s. The spatial processes described here differ from those suggesting that environmental regime shifts lead to progressive increase--decrease of stock abundance associated with homogeneous expansion-contraction of its distribution range around a fixed geographical center. Sardine population changes are seemingly related to environmental variability, whereas the spatial pattern of abundance for the northern anchovy (Engraulis mordax) appears to be inversely related to sardine population abundance. Anchovies increased where and when sardines were either absent or at a low population level. Thus, from the long-term and large-scale perspective, neither sardine nor anchovy populations conform to the simple homogeneous geographical range changes usually assumed. The sardine population changes its location within the ocean habitat in an evolving progression over a multidecadal time scale. [ABSTRACT FROM AUTHOR]