Comptes Rendus de l Académie des Sciences - Series III - Sciences de la Vie

Abstract Phytoplankton play a crucial role in marine food webs as they supply essential fatty acids (FA) to higher trophic levels, from small pelagic fish to top predators, through the intermediary action of zooplankton. Thus, the composition and nutritional value of plankton communities expectably influence abundance and condition of predators potentially leading to spatial variation in trophic transfer. Through the analysis of the FA profile of zooplankton and European sardine (Sardina pilchardus), and of the community composition of phytoplankton and zooplankton, we investigated (i) large-scale spatial variability in the trophic transfer of FA from plankton to small pelagic fish and (ii) the factors influencing this transfer in the English Channel. We found that the FA composition of zooplankton and sardine differed between the western and eastern basins of the English Channel (WEC and EEC, respectively), reflecting differences in plankton community composition. The FA profile of sardine varied further with regard to energy allocation strategies and conditions. This suggests a strong bottom-up influence of plankton community composition on the spatial variability of FA transfer with an additional impact of fish physiological status. Understanding the reasons behind the separation pattern of sardines between the WEC and the EEC would be helpful to inform fisheries and ecosystem-based management advice.

Abstract Seaweed is a potential source of sustainable food, feed, cosmetics, biomaterials, and biostimulants. Seaweed is currently mainly grown in Asia, and it is unclear which seaweed systems are best suited for North-West European waters. We use an expert workshop and a written feedback round to identify prospective seaweed systems, including the cultivation site and post-harvest stages, for three different contexts. Independent of the context, there is a preference for cultivating multiple species and having a high level of automation. Depending on the context, the optimal choice with regards to scale, substrate, seeding technique, and the integration of seaweed farming with (shell)fish species differs. Profitability of the systems, availability of (large-scale) processing facilities and ships to go offshore, uncertainty of buyers, and obstacles in seed stock availability, permits, and building infrastructures present key challenges and risks. The identified seaweed systems serve as input to the policy debate around alternative resource production in Europe and can help in developing standards for seaweed system design. Furthermore, researchers and technology providers can use the prospective systems for future profitability assessments and directions for technology developments.

Abstract Estimates of stock size for a specific year change when a new year of data is added to a stock assessment model, and some assessments exhibit a unidirectional pattern to these retrospective differences. Assuming that the most recent stock assessment is the most reliable, retrospective patterns are often misinterpreted as a measure of estimation bias that can be corrected. The logical fallacy of this interpretation is exposed when another new year of data is added, and the estimates that were assumed to be true are now considered to be biased. True values of estimated parameters are needed to infer bias. For example, simulation-estimation experiments can produce retrospective patterns from misspecified estimation models that assume time-varying processes are stationary. These simulations show that retrospective patterns are not a reliable measure of bias, and retrospective adjustments may be further from true values. Therefore, the terminology of retrospective “bias” and “correction” is misleading. Retrospective patterns can be an informative diagnostic to identify and confront model misspecification, and if retrospective patterns cannot be reduced with respecified models, they can be communicated as measure of uncertainty for consideration in the precautionary management.

Abstract The Arctic Council has identified and delineated 18 large marine ecosystems (LMEs) to provide a basis for the implementation of the ecosystem approach to management (EAM) in the Arctic. However, the ‘natural boundaries’ of these LMEs largely misalign with the ‘artificial boundaries’ established under the United Nations Convention on the Law of the Sea (UNCLOS). This raises the question of how EAM could be effectively implemented across diverse and multiple jurisdictions of the Arctic LMEs. By visualising the so-called jurisdictional situation of all 18 Arctic LMEs, this food-for-thought article highlights the inequitable and delicate position that the zonal approach of UNCLOS creates for the protection of Arctic LMEs.

Abstract Environmental and biological factors influencing fish larvae can drive fishery cohort strength, yet larval abundance is typically a better indicator of spawning biomass. Under a changing ocean, studies that explore the relationships between environmental variables, larval abundance, and fishery recruitment remain valuable areas for ongoing research. We focus on a popular, recreational-only, multispecies saltwater bass fishery (genus Paralabrax) whose population status and recovery potential are uncertain. We resolved Paralabrax spp. larval data to species over a 54-year period (1963–2016) and used species distribution models to (i) generate and test species-specific standardized indices of larval abundance as indicators of adult stock status and fishery recruitment and (ii) evaluate long-term spatiotemporal trends in their population dynamics relative to environmental variables and climate forcing. Contrary to initial hypotheses, species-specific larval abundance predicted future catches, with higher recent larval abundances suggesting potential for fishery recovery. Temperature, zooplankton biomass, and isothermal depth were important predictors of bass larval abundance, indicating these variables could also be valuable for predicting fishery recruitment and anticipating population change. Our findings paint a path forward towards a more ecosystem-based fishery management approach for this important fishery and may serve as a template for data- or assessment-limited fisheries.

Abstract The combination of animal-borne telemetry and oceanographic sensor technologies creates an opportunity for marine animals to serve as ocean observing platforms (OOPs), carrying tags that record in situ oceanographic data as they naturally move. In this study, we create a blueprint of shark OOP species selection, quantifying and comparing the potential for species to transmit collected data, the environmental ranges various candidates are expected to encounter, and the oceanographic features they may be expected to resolve. Metrics of data satellite transmission probability, movement behaviors, and environmental sampling ranges are calculated combining historically collected satellite tag data for 11 shark species tagged in the Atlantic and Pacific Ocean basins. Species with the highest satellite data transmission potential include shortfin mako (Atlantic and Pacific) and blue (Pacific) sharks. These species also demonstrated overlap in time and length scales for area-restricted search-like movement behaviors with several mesoscale ocean features, including hurricanes and upwelling events. Additional comparisons of decorrelation time scales between theoretical shark versus glider sampling platforms suggest that shark OOPs have the ability to provide three times more uncorrelated water column temperature and conductivity profiles than gliders at 15% of the operational cost.

Abstract Depredation (i.e. partial removal of target catch prior to retrieval) caused by sharks is a prevalent issue affecting several fisheries in the southeastern USA. While US fisheries managers have begun monitoring shark depredation in commercial fisheries, there have been few attempts to quantify these interactions in the recreational fishing sector. To address this knowledge gap, we initiated a citizen-science-based project to provide an in-depth characterization of shark depredation in Florida’s recreational fisheries. This was done via multiple approaches, including social media content analysis, online angler surveys, and cooperative fishery-dependent charters. Across methodologies, snapper-grouper species were the most frequently depredated target species group, and bull and sandbar sharks were the most commonly identified depredating species. Forty-three percent of anglers experienced depredation, and the probability of experiencing depredation ranged from 10% to 60% and varied both regionally and seasonally. In addition, average depredation rates ranged from 31% to 47% and were within the range of reported rates from other recreational fisheries. These results will help build a comprehensive understanding of this human-wildlife conflict and could aid fishery managers in developing management measures to address this fisheries conflict. Furthermore, this study highlights the benefit of incorporating citizen science when addressing complex fisheries issues involving stakeholder conflict.

Abstract In this study, we evaluated how well DNA metabarcoding of environmental samples captures changes in marine mesozooplankton community composition to optimize the use of sequencing data for studying seasonal dynamics. Although DNA metabarcoding is increasingly used to monitor the distribution of marine communities, there is a lack of standardized methods, and it remains uncertain to what extent the DNA data reflects patterns of community dynamics observed by other methods. Zooplankton net samples were collected every second week throughout 2017 in the northern Salish Sea, British Columbia. We compared metabarcoding of two genetic markers (18S targeting eukaryotes and cytochrome oxidase I targeting invertebrates) with microscopic assessments of the zooplankton collected. We also evaluated how data transformation using relative abundance, presence/absence, and the eDNA-index, affects the linearity between the morphological and genetic methods. Despite low taxonomic agreement between DNA metabarcoding and microscopy, we found most biomass dominating genera to be well represented. Using the eDNA-index, we found a generally good congruence between the seasonal cycles observed with microscopy and DNA, and that discrete water samples analyzed with DNA metabarcoding can provide information on the vertical distributions of mesozooplankton genera. We conclude by presenting guidelines for future studies that aim to use DNA to study marine zooplankton community dynamics.

Abstract Marine capture fisheries are crucial for many coastal communities in Malaysia and Singapore. However, knowledge of the historical state of the marine fishing resources, particularly during the British colonial period, remains limited. We compiled annual species landing data and fishing metrics from colonial and contemporary fishery reports spanning 114 years, from 1907 to 2021. Our results revealed a steady increase in species landings over 90 years, peaking in 2016 before declining in recent years. Through three case studies, we highlight high colonial landings of fusiliers (Caesionidae) from Singapore, reflecting extensive fishing operations across Southeast Asia. Bayesian Change Point analyses also identified increases in lobster landings along the east coast of Peninsular Malaysia in the mid-1980s, with fishing operations expanding from Johor northward through Pahang and Terengganu. Granger-causality tests revealed significant associations between Indian mackerel landings and the number of powered fishing boats in Perlis and Kedah in western Peninsular Malaysia, with varying lag intervals among each state. While these results enhance our understanding of fisheries trends, spatial expansion of fisheries and technological changes complicate the interpretation of fishery trends. Our results suggest that the plateau in global fishery landings since the 1980s may also have already occurred in Southeast Asia.

Abstract Vertical buoy lines (VBLs) between surface markers and bottom fishing gear frequently entangle large whales. These lethal and sublethal entanglements inhibit North Atlantic right whale (Eubalaena glacialis) recovery. Consequently, the use of persistent VBLs in situations of high entanglement risk off the east coasts of the USA and Canada is periodically prohibited. On demand, acoustic recovery systems make it possible to remove persistent VBLs, reducing entanglement risk, and potentially allowing fisheries to operate in such areas. To address concerns about performance, reliability, and safety, we evaluated numerous on-demand systems under normal fishing conditions. In 2020, conservationists, scientists, engineers, and lobster harvesters designed an experiment to trial on-demand systems in the New England offshore fisheries, using an open and honest dialogue while maintaining the confidentiality of data such as fishing locations. Between 2020 and 2023, 38 captains and their crews completed 5798 hauls using 431 on-demand units representing 10 different prototypes from multiple manufacturers. The geographic area expanded from limited offshore areas in 2020 to inshore, nearshore, and offshore waters in four different lobster management areas in 2022 and 2023. Trawl lengths ranged from 1 to 100 traps per trawl. Recovery success increased from 64% to 90% of hauls through the trials, although challenges remain, especially when fishing in deep waters or high current and tide locales. A parallel study is underway in Canada. The ability to ensure sustainable fisheries while significantly reducing entanglement risk is becoming a reality, with snow crabs and lobsters being sold in Canada and lobsters and Jonah crabs in the USA that were caught using experimental fishing permits and on-demand systems primarily in areas where persistent VBLs are seasonally prohibited for whale conservation.

Abstract Prey abundance and quality are dynamic in time and space, impacting predator ecology. We examine variation in species-specific krill quantity and quality as prey for humpback whales in the Northern California Current region, using generalized additive models to assess metrics including biomass and energy density derived from an integrated dataset of concurrent active acoustics, net tows, and marine mammal observations (2018–2022). Overall, prey metrics were positively correlated with humpback whale presence, with increasing trends modified by seasonal (early versus late foraging season) and spatial (continental shelf versus offshore) variation (model deviance explained 36.3%–40.8%). Biomass and energy density had strong positive effects on humpback whale presence, suggesting whales target high-quality swarms that offer more energy per lunge. Elevated Thysanoessa spinifera abundance near humpback whales suggests that they target this species, particularly in the late season when they are energetically richer than Euphausia pacifica, the region’s other abundant krill species. Environmental change may decrease krill abundance and quality, impacting humpback whales’ ability to meet energetic requirements and potentially driving changes in their distributions and exposure to anthropogenic threats. Clarifying drivers of humpback whale krill patch selection can improve species distribution models and aid managers in mitigating risk to whales.

Abstract Bowhead whales (Balaena mysticetus) are an iconic Arctic species with a critical ecological role as a top predator. Bowheads can reach up to 80 tonnes and 20 m, yet feed on zooplankton four orders of magnitude smaller. Arctic zooplankton community composition and distribution are changing, which may have direct impacts on bowhead foraging. Data on the threshold prey density for successful bowhead feeding are needed to predict these impacts. However, zooplankton densities are patchy temporally and spatially, influenced by oceanographic conditions that alter the location of energetically profitable patches. We assessed spatio-temporal patterns in zooplankton abundance and distribution using a multi-frequency echosounder following a systematic and opportunistic survey near feeding whales in Iqalujjuaq Fjord, Cumberland Sound, Nunavut (65.66°N, 65.20°W) during August 2023. Zooplankton net samples were used to validate the acoustic data. There was a strong link between copepod distribution and environmental variables (e.g. water depth and tidal cycle) (generalized additive models, P < .001). Copepods were present in 49.8% of the fjord, with a median density of 3240 copepods m−3 and 0.26 g C m−3. Based on published prey density requirements, this site provides feeding opportunities for juveniles but is insufficient for the needs of adults (>0.44 g C m−3).

Abstract The 5th International Conference on the Effects of Climate Change on the World’s Ocean (ECCWO5) was held from April 17 to 21, 2023, in Bergen, Norway. Some seven hundred ocean experts from around the world gathered online and under the sunny blue sky at Bryggen, a historic waterfront harbor. The ECCWO conference series was initiated in 2008, aiming to better understand the impacts of climate change on ocean ecosystems, the services they provide, and the people, businesses, and communities that depend on them. PICES, ICES, IOC, and FAO were major sponsors and organizers of this event with the Institute of Marine Research, Norway, as the local host. The outcomes of the symposium highlighted the importance of tipping points and the fact that the effects of climate change on habitat-building species are dramatic and are impacted by marine heat waves. A robust and adaptive ecosystem approach to fisheries management under climate change is recommended, and low-emission fishing should be implemented broadly. The effects of climate change on ocean deoxygenation need more research. Climate impact assessments should be routinely performed for key ecosystem components. There needs to be more focus on social-ecological approaches and effective stakeholder engagement. We encourage work across the boundaries of disciplines and geography to ensure rapid development and uptake of good practices in science-based advice and management so that they can be adopted by the fishing and aquaculture industry. The ECCWO conference series has contributed to building and maintaining a research community centered on climate change effects on the ocean that will be important moving forward.