ICES Journal of Marine Science: Journal du Conseil

Durif, C M F; Arts, M; Bertolini, F; Cresci, A; Daverat, F; Karlsbakk, E; Koprivnikar, J; Moland, E; Olsen, E M; Parzanini, C; Power, M; Rohtla, M; Skiftesvik, A B; Thorstad, E; Vøllestad, L A; Browman, H I

doi: 10.1093/icesjms/fsad149pmid: N/A

Anguillid eels were once considered to be the classic example of catadromy. However, alternative life cycles have been reported, including skipping the freshwater phase and habitat shifting between fresh, brackish, and saltwater throughout the growth phase. There is a lack of knowledge regarding these alternate life strategies, for example, the proportion of individuals in the population that adopt them compared to classic catadromy. We provide a description of these alternate life cycle strategies in temperate anguillids, their possible drivers, and the methods available to investigate them. These methods (lethal and non-lethal), include otolith microchemistry, fatty acid and stable isotope analyses, parasite identification, blood transcriptomics, and electronic tags. We argue that since the current management framework for the European eel and other temperate eels is based mainly on the freshwater component of the population, it ignores eels growing in saline waters. Many of the factors that are thought to be responsible for the precipitous decline of the eel population are more prevalent in freshwater systems. Therefore, the contribution of saline eels may be more important than currently estimated. The habitat-shifting ability of eels may be all the more crucial for the persistence and recovery of those species that are endangered.

Maltby, K M; Mason, J G; Cheng, H; Fay, G; Selden, R L; Williams, L; Alves, C L

doi: 10.1093/icesjms/fsad151pmid: N/A

Climate change is increasingly impacting marine fisheries worldwide. Concurrently, scientific interest has grown to understand how these systems can cope and adapt, with research shifting from examining vulnerability to assessing risks to focusing on determining and operationalizing resilience. As fisheries-climate-resilience researchers and practitioners navigating a sea of frameworks, toolkits, strategies, policy goals, and management desires, we take stock to ask: what does resilience mean to us? Drawing on our experiences in the northeast United States, we discuss the challenges and ambiguity we encounter in concepts of social-ecological resilience and explore implications for research and implementation. We bring together perspectives to discuss various approaches to resilience, highlighting shared and unique challenges we face. We outline three key considerations as we move forward in resilience research and practice: (1) the need for greater transparency and reflexivity among researchers regarding how they frame and approach resilience; (2) the value of increasing coordination and communication among fisheries groups working on these topics; and (3) the use of co-developed and co-produced resilience research and strategies. We urge for greater centring of communities in these discussions and to explicitly consider how resilience interacts with equity outcomes.

Kluger, L C; Garteizgogeascoa, M; Gonzales, I E; Odar, L A; Flitner, M; Damonte, G

doi: 10.1093/icesjms/fsad140pmid: N/A

The coastal waters off Peru are among the world’s most productive, thanks to the Humboldt Current and its strong coastal upwelling. Fisheries and an ever-expanding mariculture sector provide millions of Peruvians livelihoods, income, and nutrition. Coastal communities engaging with these sectors face a volatile environment they have historically adapted to. But when the COVID-19 pandemic unfolded in 2020, affecting all aspects of life, challenges for the fisheries and mariculture sectors emerged to a yet unprecedented extent. This work applies a mixed-method approach for documenting and analysing the effects of the pandemic on the Peruvian seafood sector and seafood worker’s economy in particular. Mobility restrictions and market closures disrupted seafood supply chains, altering access to nutrition and income for many people involved. Interviewees aimed to diversify livelihood strategies and use personal networks to withstand the crisis, while some established adaptation strategies, such as migration towards other fishing grounds, were largely impeded. Our results highlight the vulnerability of seafood value chains—mainly artisanal and small-scale fisheries—in the face of such a global crisis. The implications of the pandemic for the long-term sustainability of Peruvian coastal–marine activities are discussed and set into the context of previously experienced crises in the region.

Blamey, Laura K; Plagányi, Éva E; Robins, Julie; Kenyon, Rob; Deng, Roy A; Hughes, Justin; Kim, Shaun

doi: 10.1093/icesjms/fsad144pmid: N/A

Anthropogenic alterations to river flow could have repercussions for flow-dependent species downstream but few studies account for these dynamic relationships or quantify impacts of altered river flow. Scylla serrata—a widely distributed portunid crab—was used as an example of a flow-dependent species to model impacts of altered flow on species abundance and catch. Crab population dynamics were modelled across a large semi-enclosed tropical sea in northern Australia. Environmental drivers, primarily river flow, but also temperature and the Southern Oscillation Index were linked to crab dynamics to explain variability in historical catches. Catch and abundance could then be predicted under altered flow scenarios. River flow significantly improved the ability to explain historical catches for some regions but not all, and the strength of this relationship varied across catchments. Altered flows had negligible effects for perennial rivers but for ephemeral and temporally variable rivers, predicted decreases in abundance and catch ranged from 36 to 46% on average. Our modelling approach showcases a way to dynamically and rigorously quantify impacts of altered river flow on a key species with potential to help inform natural resource management, including policy decisions on the timing, quantity, and method of water removed from rivers.

Sakamoto, Tatsuya; Horii, Sachiko; Kodama, Taketoshi; Takahashi, Kazutaka; Tawa, Atsushi; Tanaka, Yosuke; Ohshmio, Seiji

doi: 10.1093/icesjms/fsad145pmid: N/A

Knowledge of the movements of marine organisms is essential for effective conservation schemes. Here, we investigated the lifetime habitat use of diamond squid, Thysanoteuthis rhombus, collected in the western North Pacific and its marginal seas (the Sea of Japan and the East China Sea) during 2021–2022, whose migratory ecology is poorly known, using bulk stable nitrogen and carbon isotope ratios in eye lenses. From the eye lens isotope profiles, the chronology of the isotopic baseline of squid habitat was estimated by removing the effect of size-dependent changes of trophic position. Then, the baseline estimates were compared to the isoscapes of particulate organic matter. The baseline chronologies showed fluctuations during the paralarval and juvenile stages, becoming stable during the adult stage, suggesting that significant movements mainly occur during the early life stages due to current transport, with adults potentially not undertaking long-distance migrations. The squids in the marginal seas mostly originated from outside the subtropical gyre, while the squids in the subtropical gyre had various sources, including outside the gyre and southern and northern parts within the gyre, revealing a complex mixing pattern of the species. These results show that isotope chronology combined with baseline isoscapes are effective tools to understand animal migrations, which can help managing various cephalopods and fish.

Silvar-Viladomiu, Paula; Minto, Cóilín; Lordan, Colm; Brophy, Deirdre; Bell, Rich; Collie, Jeremy; Reid, David

doi: 10.1093/icesjms/fsad146pmid: N/A

The Celtic Seas ecoregion (CSE) is undergoing climatic and ecosystem changes, which can induce changes in fish productivity. Globally, the productivity of many stocks has shown evidence of change over decadal timescales. Varying factors might drive these dynamics in the CSE, but for many stocks, these mechanisms have not been fully understood to be included in management advice. We study dynamic productivity for 28 stocks in the Celtic Seas by tracking integrated stochastic signals in the relationship between stock size and recruitment using state-space modelling applying Peterman’s Productivity Method. Our research objectives were to (i) fit Ricker stock–recruitment models with time-varying parameters to all age- or length-based assessed stocks in the CSE, (ii) evaluate which parameters vary in time, (iii) examine temporal characteristics of historical recruitment productivity, and (iv) evaluate productivity correlation across stocks. For 22 out of 28 stocks, at least one of the three time-varying parameter models had a better fit than the time-invariant model. In the CSE, fish productivity has diverse temporal patterns, with some stocks displaying relevant long-term decreasing productivity trends. Getting insight into temporal changes in recruitment productivity is very valuable and has important implications for sustainable fisheries.

Groner, M L; Bravo-Mendosa, E D; MacKenzie, A H; Gregg, J L; Conway, C M; Trochta, J T; Hershberger, P K

doi: 10.1093/icesjms/fsad147pmid: N/A

Causes of population collapse and failed recovery often remain enigmatic in marine forage fish like Pacific herring (Clupea pallasii) that experience dramatic population oscillations. Diseases such as ichthyophoniasis are hypothesized to contribute to these declines, but lack of long-term datasets frequently prevents inference. Analysis of pathogen surveillance and population assessment datasets spanning 2007–2019 indicate that the age-based prevalence estimate of Ichthyophonus infection was, on average, 54% greater among a collapsed population of Pacific herring (Prince William Sound, Alaska, USA) as compared to a nearby population (Sitka Sound, Alaska, USA) that is relatively robust. During the study years, the age-based infection prevalence ranged from 14 to 44% in Prince William Sound and 5 to 33% in Sitka Sound. At both sites, the age-based infection prevalence declined over time, with an average decrease of 7% per year. Statistical analyses indicated that infection prevalence between the two populations was reduced by regional factors affecting both sites, and that these factors were independent of herring density. Infection prevalence in both populations was positively correlated with herring age and negatively correlated with the Pacific Decadal Oscillation. This study demonstrates how synthesis of environmental, stock assessment, and disease assessment data can be leveraged to elucidate epidemiological trends in diseases of wild fish.

López, N A; McAuley, R B; van Elden, S; Meeuwig, J J

doi: 10.1093/icesjms/fsad153pmid: N/A

Scalloped hammerhead sharks Sphyrna lewini are threatened throughout their distribution. The species forms aggregations, which can potentially increase its vulnerability to human impacts. Identification and characterization of aggregation sites are essential to inform management and conservation. We used drones to characterize the spatial and temporal distribution of a recently documented scalloped hammerhead aggregation within the Shoalwater Islands Marine Park, in southwest Western Australia. A total of 267 drone transects were conducted across the Austral summers of 2019–2020 and 2020–2021. The presence or absence of the sharks was examined in relation to fine scale patterns in habitat type, environmental conditions, and the occurrence of human activities. Scalloped hammerhead sharks had a small spatial and temporal distribution within the study area. Their presence in the study area was higher on days associated with higher lunar illumination phases, which could indicate that the aggregation site is potentially acting as a refuge for resting and/or predatory avoidance. The extent to which human interactions affect scalloped hammerhead sharks at the aggregation site remains unclear and raises questions about the adequacy of management measures at Shoalwater Islands Marine Park. Recommendations are proposed to limit potential impacts, such as establishing spatiotemporal fishing restrictions and regulating public interactions.

Yalcin, Semra; Anderson, Sean C; Regular, Paul M; English, Philina A

doi: 10.1093/icesjms/fsad155pmid: N/A

Indices of abundance derived from fisheries-independent surveys play a crucial role in sustainable fisheries management. While design-based methods provide unbiased indices in theory, logistical constraints may introduce biases in practice. Spatiotemporal models offer potential for mitigating such bias, but their limitations remain poorly understood. In this study, we compare the performance of model-based and design-based indices using 200 simulated populations representing two virtual species. We simulate stratified-random surveys under various scenarios, including constant effort and coverage, reduced set density, and reduced spatial coverage (e.g. closed areas). We consider three closed-area scenarios: no population recovery, population recovery, and population recovery with spillover. With consistent survey coverage, correctly specified spatiotemporal models demonstrated comparable bias, accuracy, and confidence interval coverage to design-based methods. Spatiotemporal models incorporating appropriate covariates and observation families could mitigate the impact of reduced spatial coverage. However, poorly specified models were sometimes outperformed by design-based methods. Our results, therefore, highlight the potential for spatiotemporal models to mitigate the effects of survey effort reduction on population assessment and the provision of scientific advice. However, they also present a cautionary tale about the critical importance of model evaluation and comparison.

Votier, S C; Sherley, R B; Scales, K L; Camphuysen, K; Phillips, R A

doi: 10.1093/icesjms/fsad173pmid: N/A

Knowledge of fisheries impacts, past and present, is essential for understanding the ecology and conservation of seabirds, but in a rapidly changing world, knowledge and research directions require updating. In this Introduction and in the articles in this Themed Set “Impacts of fishing on seabirds”, we update our understanding of how fishing impacts seabird communities and identify areas for future research. Despite awareness of the problems and mitigation efforts for >20 years, fisheries still negatively impact seabirds via the effects of bycatch, competition, and discards. Bycatch continues to kill hundreds of thousands of seabirds annually, with negative population-level consequences. Fisheries for forage fish (e.g. anchovy, sandeel, and krill) negatively impact seabirds by competing for the same stocks. Historically, discards supplemented seabird diets, benefitting some species but also increasing bycatch rates and altering seabird community composition. However, declining discard production has led to potentially deleterious diet switches, but reduced bycatch rates. To improve research into these problems, we make the following recommendations: (1) improve data collection on seabird–vessel interaction and bycatch rates, on fishing effort and vessel movements (especially small-scale fleets), and on mitigation compliance, (2) counter the current bias towards temperate and high-latitude ecosystems, larger-bodied species and particular life stages or times of year (e.g. adults during breeding), and (3) advance our currently poor understanding of combined effects of fisheries and other threats (e.g. climate change, offshore renewables). In addition, research is required on under-studied aspects of fishing impacts: consequences for depleted sub-surface predators, impacts of illegal, unreported and unregulated fishing, artisanal and emerging fisheries, such as those targeting mesopelagic fish, have received insufficient research attention. Some of these shortfalls can be overcome with new tools (e.g. electronic monitoring, remote sensing, artificial intelligence, and big data) but quantifying and addressing fishing impacts on seabirds requires greater research investment at appropriate spatio-temporal scales, and more inclusive dialogue from grassroots to national and international levels to improve governance as fishing industries continue to evolve.