Migratory behaviour and range in Atlantic cod: inference from a century of tagging

A century of tagging experiments on 174 Atlantic cod (Gadus morhua) groups is reviewed and the frequency and spatial distribution of four migratory behaviours documented. Of all cod groups, 41% were categorized as sedentary, 18% as accurate homers, 20% as inaccurate homers and 20% as dispersers (ranging over large areas without recognizable return migrations). All behaviours occurred over the full spatial range of cod. Coastal groups did not differ significantly from offshore (shelf) groups in the relative frequency of migratory behaviours. However, the north‐east Atlantic had more sedentary and accurate homing groups than did the north‐west Atlantic, which had more dispersing groups. Overall, sedentary cod groups had lower maximum historical biomass than did other groups, confirming that migration/dispersal begets abundance. Maximum historical biomass was strongly related to the area occupied [log (biomass, tonnes)] = 1.58 log (range, km²) + 1.529; r² = 0.9), irrespective of migratory type (for 23 major groups a total of 22 million tonnes over 3.3 million km² with an average density of 7 tonnes km^?2). Historical densities were not related to area occupied, although all large groups exhibited high densities (10–12 tonnes km^?2 ; smaller groups had a wide range of density). The four migratory strategies in cod enable entrainment by diverse physical, oceanographic and biological ecosystem properties, and is key to cod success in the North Atlantic.     

Fishing impact and environmental status in European seas: a diagnosis from stock assessments and ecosystem indicators

Stock‐based and ecosystem‐based indicators are used to provide a new diagnosis of the fishing impact and environmental status of European seas. In the seven European marine ecosystems covering the Baltic and the North‐east Atlantic, (i) trends in landings since 1950 were examined; (ii) syntheses of the status and trends in fish stocks were consolidated at the ecosystem level; and (iii) trends in ecosystem indicators based on landings and surveys were analysed. We show that yields began to decrease everywhere (except in the Baltic) from the mid‐1970s, as a result of the over‐exploitation of some major stocks. Fishermen adapted by increasing fishing effort and exploiting a wider part of the ecosystems. This was insufficient to compensate for the decrease in abundance of many stocks, and total landings have halved over the last 30 years. The highest fishing impact took place in the late 1990s, with a clear decrease in stock‐based and ecosystem indicators. In particular, trophic‐based indicators exhibited a continuous decreasing trend in almost all ecosystems. Over the past decade, a decrease in fishing pressure has been observed, the mean fishing mortality rate of assessed stocks being almost halved in all the considered ecosystems, but no clear recovery in the biomass and ecosystem indicators is yet apparent. In addition, the mean recruitment index was shown to decrease by around 50% in all ecosystems (except the Baltic). We conclude that building this kind of diagnosis is a key step on the path to implementing an ecosystem approach to fisheries management.     

Multi‐decadal climate and fishing predictors of abundance for U.S. South Atlantic coastal fishes and invertebrates

Abundance of marine stocks fluctuates in response to both internal processes (e.g., density dependence) and exogenous drivers, including the physical environment, fishing, and trophodynamic interactions. In the United States, research investigating ecosystem drivers has been focused in data‐rich systems, primarily in the North Atlantic and North Pacific. To develop a more holistic understanding of important ecosystem drivers in the Southeast U.S. continental shelf Large Marine Ecosystem, we applied generalized linear and dynamic linear modeling to investigate the effects of climate and fishing covariates on the relative abundance trends of 71 demersal fish and invertebrate species sampled by a coastal trawl survey during 1990–2013. For the assemblage as a whole, fishing effects predominated over climate effects. In particular, changes in trawling effort within the penaeid shrimp fishery governed abundance trends of bony fishes, invertebrates, and elasmobranchs, a likely result of temporal changes in bycatch mortality. Changes in trawling intensity induced changes in overall community composition and appear to have altered trophic interactions among particular species. Among climate indices investigated, the Pacific Decadal Oscillation and the Western Bermuda High Index were most prevalent in well‐supported dynamic linear models. Observed annual abundance trends were synchronous among some taxonomically related species, highlighting similar responses to exogenous influences based on life history. This study strengthens the foundation for generating hypotheses and advancing ecosystem‐based fisheries research within the region.     

Links between the recruitment success of northern European hake (Merluccius merluccius L.) and a regime shift on the NE Atlantic continental shelf

The distribution of northern European hake (Merluccius merluccius L.) extends from the Bay of Biscay up to Norwegian waters. However, despite its wide geographical distribution, there have been few studies on fluctuations in the European hake populations. Marine ecosystem shifts have been investigated worldwide and their influence on trophic levels has been studied, from top predator fish populations down to planktonic prey species, but there is little information on the effect of atmosphere–ocean shifts on European hake. This work analyses hake recruitment success (recruits per adult biomass) in relation to environmental changes over the period 1978–2006 in order to determine whether the regime shift identified in several abiotic and biotic variables in the North Sea also affected the Northeast Atlantic shelf oceanography. Hake recruitment success as well as parameters such as the sea surface temperature, wind patterns and copepod abundance changed significantly at the end of the 1980s, demonstrating an ecological regime shift in the Northeast Atlantic. Despite the low reproductive biomass recorded during the last decades, hake recruitment success has been higher since the change in 1989/90. The higher productivity may have sustained the population despite the intense fishing pressure; copepod abundance, warmer water temperatures and moderate eastward transport were found to be beneficial. In conclusion, in 1988/89 the Northeast Atlantic environment shifted to a favourable regime for northern hake production. This study supports the hypothesis that the hydro‐climatic regime shift that affected the North Sea in the late 1980s may have influenced a wider region, such as the Northeast Atlantic.     

Contribution of bait to lobster production in an oligotrophic marine ecosystem as determined using a mass balance model

The fishery for the western rock lobster (Panulirus cygnus) in Western Australia is Australia's largest trap-based fishery, deploying 8.8 million pot lifts, landing on average 11,000 tonnes of lobster and using approximately 14,000 tonnes of bait annually. A mass balance model was constructed to determine the potential contribution of this bait to the diet of western rock lobsters. Bait is potentially a significant subsidy given the oligotrophic nature of Western Australia's marine environment. The mass balance model was constructed on the principle that the biomass of the lobster population reflects the difference between inputs (growth, immigration) and outputs (natural and fishing mortality and emigration). Biomass calculated using this approach was within 7% of biomass calculated from independent estimates based on depletion analysis, indicating the model is robust. The food required to explain observed growth was then calculated, allowing the potential contribution of bait to lobster diet to be assessed. The abundance of natural diet items on the benthos was sufficient to explain the observed growth of lobsters, with bait contributing a maximum of 13% of lobster food requirements over the whole ecosystem. This contribution of bait will differ spatially and temporally reflecting uneven distribution of fishing effort and may be as high as 35% during some months of the fishing season, a result consistent with dietary studies based on stable isotopes. Given observed effects of organic matter addition on ecosystem processes as observed in trawl fisheries and aquaculture operations, it is likely that the effects of bait addition on ecosystem function are more widespread than lobster production.     

Productivity and recovery of forage fish under climate change and fishing: North Sea sandeel as a case study

Forage fish occupy a central position in marine food‐webs worldwide by mediating the transfer of energy and organic matter from lower to higher trophic levels. The lesser sandeel (Ammodytes marinus) is one of the ecologically and economically most important forage fish species in the North‐east Atlantic, acting as a key prey for predatory fish and sea birds, as well as supporting a large commercial fishery. In this case study, we investigate the underlying factors affecting recruitment and how these in turn affect productivity of the North Sea sandeel using long‐term data and modelling. Our results demonstrate how sandeel productivity in the central North Sea (Dogger Bank) depends on a combination of external and internal regulatory factors, including fishing and climate effects, as well as density dependence and food availability of the preferred zooplankton prey (Calanus finmarchicus and Temora longicornis). Furthermore, our model scenarios suggest that while fishing largely contributed to the abrupt stock decline during the late 1990s and the following period of low biomass, a complete recovery of the stock to the highly productive levels of the early 1980s would only be possible through changes in the surrounding ecosystem, involving lower temperatures and improved feeding conditions. To that end, we stress the need for ecosystem‐based management accounting for multiple internal and external factors occurring within the broader context of the ecosystem in which forage fish species, such as sandeel, play an important and integral part.     

Comparing the roles of Pacific halibut and arrowtooth flounder within the Gulf of Alaska ecosystem and fishing economy

The fishing industry of the western and central regions of the coastal Gulf of Alaska (CGoA) directly employs over 17,000 people and processes fish with a wholesale value of US$618 million annually. Pacific halibut (Hippoglossus stenolepis) are a valued groundfish species because of the high quality of their flesh. In contrast, arrowtooth flounder (Atheresthes stomias) are much more abundant but of low value because their flesh degrades upon heating. Both are high trophic level predators but play different roles in the ecosystem because of differences in abundance and diet. Using an end‐to‐end ecosystem model, we evaluate the impact of alternate levels of fishing effort and large‐scale changes in oceanographic conditions upon both species, the ecosystem, and the fishing economy. Reduction of longline efforts to reduce Pacific halibut mortality led to reduction in total value of all CGoA landings but increase in value landed by sport fisheries, trawl fleets, and fish pot vessels as they exploit a greater share of available halibut, sablefish, and Pacific cod. Increased trawl effort to raise arrowtooth flounder mortality led to increase in total value of all landings but large reductions in value landed by longline, jig, fish pot, and sport fleets with greater competition for available Pacific cod, halibut, and sablefish. Oceanographic conditions that enhance pelagic food chains at the expense of benthic food chains negatively impact groundfish in general, though Pacific halibut and arrowtooth flounder are resilient to these effects because of the high importance of pelagic fish in their diets.     

The role of sand lances (Ammodytes sp.) in the Northwest Atlantic Ecosystem: A synthesis of current knowledge with implications for conservation and management

The American sand lance (Ammodytes americanus, Ammodytidae) and the Northern sand lance (A. dubius, Ammodytidae) are small forage fishes that play an important functional role in the Northwest Atlantic Ocean (NWA). The NWA is a highly dynamic ecosystem currently facing increased risks from climate change, fishing and energy development. We need a better understanding of the biology, population dynamics and ecosystem role of Ammodytes to inform relevant management, climate adaptation and conservation efforts. To meet this need, we synthesized available data on the (a) life history, behaviour and distribution; (b) trophic ecology; (c) threats and vulnerabilities; and (d) ecosystem services role of Ammodytes in the NWA. Overall, 72 regional predators including 45 species of fishes, two squids, 16 seabirds and nine marine mammals were found to consume Ammodytes. Priority research needs identified during this effort include basic information on the patterns and drivers in abundance and distribution of Ammodytes, improved assessments of reproductive biology schedules and investigations of regional sensitivity and resilience to climate change, fishing and habitat disturbance. Food web studies are also needed to evaluate trophic linkages and to assess the consequences of inconsistent zooplankton prey and predator fields on energy flow within the NWA ecosystem. Synthesis results represent the first comprehensive assessment of Ammodytes in the NWA and are intended to inform new research and support regional ecosystem‐based management approaches.     

Shifting trophic architecture of marine fisheries in New Zealand: Implications for guiding effective ecosystem‐based management

New Zealand has led the world in restoration of marine fisheries since the introduction of the Quota Management System in 1986, but challenges remain in minimizing the ecosystem‐level effects of industrialized fishing. We analysed existing long‐term fisheries data sets from 1931 to 2015 in New Zealand to resolve trends in important ecological properties of major exploited fish communities. Increases in community dissimilarities of catch composition in 1931 and 1972, followed by increasing total landings, highlight major expansions of fishing grounds and exploited species during these periods. Mirroring global patterns, the remarkable rise in fishing power, demand and generation of new markets in New Zealand have all contributed to this expansion. Marine Trophic Indices (MTIs) of landings have decreased together with total catch after the year 2000, reflecting smaller catches with a higher composition of lower trophic‐level species in recent years. Differences in relative abundance of species estimated between fisheries‐dependent and fisheries‐independent data were observed, where high‐value species displayed better agreement in relative abundance between data sets. Despite being under a Quota Management System, temporal development of MTI values relative to the timing of industrial expansion of fisheries was remarkably similar to those observed in the North Sea and Brazil, with a single expansion and decline. MTI values presented better long‐term stability in the US fisheries analysed. Analysis of long‐term data and the development of well‐resolved ecological baselines will be the first step towards applying EBM to New Zealand fisheries, in keeping with global trends in fisheries management.     

Ecosystem effects of invertebrate fisheries

Since the 1950s, invertebrate fisheries catches have rapidly expanded globally to more than 10 million tonnes annually, with twice as many target species, and are now significant contributors to global seafood provision, export, trade and local livelihoods. Invertebrates play important and diverse functional roles in marine ecosystems, yet the ecosystem effects of their exploitation are poorly understood. Using 12 ecosystem models distributed worldwide, we analysed the trade‐offs of various invertebrate fisheries and their ecosystem effects as well as ecological indicators. Although less recognized for their contributions to marine food webs, our results show that the magnitude of trophic impacts of invertebrates on other species of commercial and conservation interest is comparable with those of forage fish. Generally, cephalopods showed the strongest ecosystem effects and were characterized by a strong top‐down predatory role. Lobster, and to a lesser extent, crabs, shrimp and prawns, also showed strong ecosystem effects, but at lower trophic levels. Benthic invertebrates, including epifauna and infauna, also showed considerable ecosystem effects, but with strong bottom‐up characteristics. In contrast, urchins, bivalves, and gastropods showed generally lower ecosystem effects in our simulations. Invertebrates also strongly contributed to benthic–pelagic coupling, with exploitation of benthic invertebrates impacting pelagic fishes and vice versa. Finally, on average, invertebrates produced maximum sustainable yield at lower levels of depletion (~45%) than forage fish (~65%), highlighting the need for management targets that avoid negative consequences for target species and marine ecosystems as a whole.     

Recruitment,distribution boundary and habitat temperature of an arcto‐boreal gadoid in a climatically changing environment: a case study on Northeast Arctic haddock (Melanogrammus aeglefinus)

Climate change is expected to have major effects on the distribution and abundance of fish. In spite of extensive research on the topic in high‐latitude marine ecosystems, the mechanistic understanding of how temperature impacts recruitment and distribution of arcto‐boreal fish stocks remains elusive. Exemplified by an arcto‐boreal gadoid in the Barents Sea, the Northeast Arctic (NEA) haddock (Melanogrammus aeglefinus), we investigate the effect of ecosystem temperature (here temperature from a fixed reference section) on abundance and distribution boundaries between 1981 and 2008. During this time interval there has been a trend of increasing temperature in the ecosystem. We compare the ecosystem temperature with the species habitat temperature of NEA haddock (i.e., ambient temperature of the population) – two temperature approaches representing the indirect and direct environmental impacts on fish, respectively. In addition to the temperature effects, density‐dependent effects on distribution boundaries are considered. The study is based on swept area density estimates and spatial temperature data collected annually in winter surveys. We found a positive relationship between ecosystem temperature and abundance, a connection related to both direct and indirect mechanisms with short‐term and long‐term pathways. Distribution boundaries are, on a year‐to‐year basis, more related to abundance than ecosystem temperature. The long‐term trends, however, indicate a north‐eastward shift in distribution boundaries, probably indirectly related to the coinciding ecosystem temperature increase. In spite of the gradual increase in ecosystem temperature, the abundance of 4‐ to 7‐ year old NEA haddock expanded into colder waters. Thus, our results show how different the two temperature approaches may be.     

Population ecological parameters and biomass of anchovy kilka <Emphasis Type="Italic">Clupeonella engrauliformis</Emphasis> in the Caspian Sea

ABSTRACT:   Through most of the last century, three endemic kilka species supported major commercial species in the Caspian Sea. It is clear that catches and abundance of all species have changed, but catch and sampling data are limited and stock assessments are inadequate. Recent changes in the Caspian Sea ecosystem have occurred as a consequence of climatic environmental change (sea level change) and ecologic change caused by the invasive ctenophore Mnemiopsis leidyi . This paper examines the effects of these changes on the population biology and biomass of anchovy kilka Clupeonella engrauliformis in Iranian waters of the Caspian Sea from 1995 to 2004. For most years during this 10-year period, we estimated the age structure of catch, length–weight relationship, von Bertalanffy growth parameters, condition factors, sex ratios, maturity stages determined from ovarian analysis, natural and fishing mortality, age at first capture, and spawning biomass. The instantaneous coefficient of natural mortality was estimated as 0.473/year and the instantaneous coefficient of fishing mortality varied during the 10-year period between 0.541 and 2.690/year. Biomass of anchovy kilka declined from about 186 000 t in 1996 to less than 12 000 t in 2004. Recent high fishing rates were not sustainable after the introduction of Mnemiopsis , so overfishing is part of the explanation for the collapse of anchovy kilka in the Caspian Sea.     

Mechanistic links between climate and fisheries along the east coast of the United States: explaining population outbursts of Atlantic croaker (Micropogonias undulatus)

Climate has been linked to variation in marine fish abundance and distribution, but often the mechanistic processes are unknown. Atlantic croaker (Micropogonias undulatus) is a common species in estuarine and coastal areas of the mid‐Atlantic and southeast coasts of the U.S. Previous studies have identified a correlation between Atlantic croaker abundance and winter temperatures in Chesapeake Bay, and have determined thermal tolerances of juveniles. Here we re‐examine the hypothesis that winter temperature variability controls Atlantic croaker population dynamics. Abundance indices were analyzed at four life history stages from three regions along the east coast of the U.S. Correlations suggest that year‐class strength is decoupled from larval supply and is determined by temperature‐linked, overwinter survival of juveniles. Using a relation between air and water temperatures, estuarine water temperature was estimated from 1930 to 2002. Periods of high adult catch corresponded with warm winter water temperatures. Prior studies indicate that winter temperature along the east coast is related to the North Atlantic Oscillation (NAO); variability in catch is also correlated with the NAO, thereby demonstrating a link between Atlantic croaker dynamics, thermal limited overwinter survival, and the larger climate system of the North Atlantic. We hypothesize that the environment drives the large‐scale variability in Atlantic croaker abundance and distribution, but fishing and habitat loss decrease the resiliency of the population to periods of poor environmental conditions and subsequent weak year classes.     

Retrospective analysis of the influence of environmental drivers on commercial stocks and fishing opportunities in the Irish Sea

Irish Sea fisheries have undergone considerable change in recent years following the decline of commercially important finfish stocks and their slow response to management's recovery plans. In 2015, the fishing industry called for a holistic exploration into the impact of environmental change and food web effects to identify the drivers underpinning stock dynamics. In this study, we identify correlations between large‐scale climatic indicators, temperature, primary and secondary productivity, and fish recruitment in the Irish Sea and incorporate them into an Ecopath with Ecosim food web model co‐created by scientists and fishers. Negative correlations were found between the North Atlantic Oscillation winter index (NAOw) and large zooplankton abundance and between the Atlantic Multidecadal Oscillation (AMO) and the recruitment of cod (Gadus morhua) and whiting (Merlangius merlangus). Using correlation analyses to direct the addition of environmental drivers to the Irish Sea ecosystem model improved the models fit against observed biomass and catch data and revealed the indirect impacts of environmental change as mitigated through trophic interactions. Model simulations suggest that historic environmental change suppressed the overall production of commercial finfish, limiting opportunities for the fishing industry, whilst also dampening the rate of stock recovery despite marked reductions in fishing effort. These results suggest that failure to account for ecosystem information may lead to misconceived expectations and flawed fisheries management; therefore, there is a need to operationalize ecosystem information through management procedures to support fisheries advice.     

Do albacore exert top‐down pressure on northern anchovy? Estimating anchovy mortality as a result of predation by juvenile north pacific albacore in the California current system

Quantifying the mortality of marine fishes is important for understanding spawner–recruit relationships, predicting year‐class strength, and improving fishery stock assessment models. There is increasing evidence that pelagic predators can exert a top‐down influence on prey, especially during critical early life‐history stages. The objective of this study was to quantify predation by North Pacific albacore on Northern anchovy in the California current system (CCS). I estimated the abundance of juvenile albacore in the CCS from 1966–2005 using stock assessment models and spatially explicit catch‐per‐unit‐effort time series. Anchovy abundance (1966–93), both recruitment and total biomass, was obtained from a stock assessment model. Annual rates of anchovy consumption by albacore were calculated using diet studies of albacore in the CCS, an age‐structured bioenergetics model, and regional estimates of albacore abundance. The range of estimates was large: albacore may remove from less than 1% to over 17% of anchovy pre‐recruitment biomass annually. Relationships between predation and recruitment biomass were consistent with expectations from top‐down effects, but further study is required. This is the first attempt to quantify a specific source of mortality on anchovy recruits and to demonstrate potential top‐down effects of predation on anchovy.     

How commercial fishing effort is managed

Wild capture fisheries produce 90 million tonnes of food each year and have the potential to provide sustainable livelihoods for nearly 40 million people around the world ( http://www.fao.org/3/a-i5555e.pdf ). After decades of overfishing since industrialization, many global fish stocks have recovered, a change brought about through effective management. We provide a synthetic overview of three approaches that managers use to sustain stocks: regulating catch and fishing mortality, regulating effort and regulating spatial access. Within each of these approaches, we describe common restrictions, how they alter incentives to change fishing behaviour, and the resultant ecological, economic and community‐level outcomes. For each approach, we present prominent case‐studies that illustrate behaviour and the corresponding performance. These case‐studies show that sustaining target stocks requires a hard limit on fishing mortality under most conditions, but that additional measures are required to generate economic benefits. Different systems for allocation allow stakeholder communities to strike a locally acceptable balance between profitability and employment.     

Bloom or bust: synchrony in jellyfish abundance,fish consumption,benthic scavenger abundance,and environmental drivers across a continental shelf

Increases in gelatinous zooplankton (GZ) populations, their dominance of some ecosystems, their impacts to other taxa, and their questionable trophic value remain global concerns, but they are difficult to quantify. We compared trends in GZ abundance from direct sampling for the northeast U.S. continental shelf and tested their association with GZ consumption by spiny dogfish (Squalus acanthias); the abundance of two benthic scavengers: Atlantic hagfish (Myxine glutinosa) and grenadiers (Family: Macrouridae); and four environmental indices: Atlantic Multidecadal Oscillation, North Atlantic Oscillation, and sea surface and bottom temperatures. Defined as scyphozoans, siphonophores, ctenophores, and salps, the abundance of GZ on the shelf has oscillated with blooms approximately every 10–15 yr. Conservative estimates of annual removal of GZ by spiny dogfish ranged from approximately 0.3–298 g individual^?1 with spiny dogfish being the primary GZ feeder sampled on the shelf. The examination of three abundance series for GZ identified one shelf‐wide trend and strong relationships with 2‐yr lagged consumption and scavenger abundance (namely hagfish), and sea surface temperature. With multimodel inference, these covariates led to an optimal model of GZ abundance. Blooms of GZ abundance on this shelf were influenced by environmental change, provide surges of food for spiny dogfish, and may offer ‘food falls’ for scavenging fishes. The bioenergetic tradeoffs of consuming greater amounts of GZ compared to other major prey (e.g., fishes) remain unknown; however, these surges of food in the northwest Atlantic appear to be important for fishes, including support for benthic scavenger productivity.     

Spatio‐temporal distribution of albacore (Thunnus alalunga) catches in the northeastern Atlantic: relationship with the thermal environment

When the spring seasonal warming starts, North Atlantic albacore (Thunnus alalunga) juveniles and pre‐adults perform a trophic migration to the northeastern Atlantic, to the Bay of Biscay and to the southeast of Ireland. During this migration, they are exploited by Spanish trolling and baitboat fleets. The present study analyzes the relationship between the albacore spatio‐temporal distribution and the thermal environment. For this approach, several analyses have been performed on a database including fishing logbooks and sea surface temperature (SST) images, covering the period between 1987 and 2003. SST values and the SST gradients at the catch locations have been statistically compared to broader surrounding areas to test whether the thermal environment determines the spatial distribution of albacore. General additive models (GAM) have been used also to evaluate the relative importance of environmental variables and fleet behaviour. The results obtained show that, although juvenile albacore catch locations are affected by fleet dynamics, there is a close spatial and temporal relationship with the seasonal evolution of a statistically significant preferential SST window (16–18°C). However, differences have been identified between the relationship of albacore with SST within the Bay of Biscay in July and August (higher temperature). Such differences are found also in the spatial distribution of the catch locations; these reflect clearly the presence of two groups, differentiated after the third week of the fishing campaign at the end of June. The analysis undertaken relating the distribution of North Atlantic albacore juveniles with thermal gradients did not provide any evidence of a relationship between these catch locations and the nearby occurrence of thermal gradients.     

Just a FAD? Ecosystem impacts of tuna purse‐seine fishing associated with fish aggregating devices in the western Pacific Warm Pool Province

The western and central Pacific Ocean supports the world's largest tuna fisheries. Since the 1990s, the purse‐seine fishery has increasingly fished in association with fish aggregating devices (FADs), which has increased catches of juvenile bigeye and yellowfin tunas and vulnerable bycatch species (e.g., sharks). This has raised concerns regarding the sustainability of these species’ populations and the supporting ecosystem, but may provide improved food security of Pacific Island nations through utilisation of FAD‐associated byproduct species (e.g., wahoo). An ecosystem model of the western Pacific Warm Pool Province was used to explore the potential ecological impacts of varying FAD fishing effort (±50% or 100%) over 30 years. The ecosystem has undergone a significant change in structure since 1980 from heavy exploitation of top predators (e.g., tunas) and “fishing up the food web” of high‐trophic‐level non‐target species. The ecosystem appeared resistant to simulated fishing perturbations, with only modest changes (<10%) in the biomass of most groups, although some less productive shark bycatch species decreased by up to 43%, which had a subsequent positive effect on several byproduct species, the prey of sharks. Reduction of FAD effort by at least 50% was predicted to increase the biomass of tuna species and sharks and return the ecosystem structure to a pre‐industrial‐fishing state within 10 years. Spatial disaggregation of the model and integration of economic information are recommended to better capture ecological and economic changes that may result from fishing and/or climate impacts and to develop appropriate management measures in response.     

Stock assessment of the blue jack mackerel,Trachurus picturatus,in the North‐eastern Atlantic

A total of 49,151 blue jack mackerel, Trachurus picturatus, (Bowdich) was collected in Madeira Island (North‐eastern Atlantic) between 2002 and 2016 to evaluate possible influence of fishing on landings and reproductive parameters. A decreasing trend in the length composition was observed over the study period and length at first maturity decreased by 2.78 cm TL. Maximum yield per recruit decreased from 2002 to 2016 but the corresponding fishing mortality was constant (F_max = 0.4/year). Considering the fishing mortality level in 2016, it is evident that the stock may be exploited beyond its sustainability limit. Amendments of the purse‐seine fishing regulations and implementation of measures to reduce fishing effort are suggested.