Large Fish Species Research Articles

Fish on the Move: Transporting and Processing Fish as Part of the Castle Economy in the Northern Baltic Sea

The importance of fish for the medieval and early modern economy in the Baltic Sea is known through separate studies by historians and archaeologists. This article aims to combine zooarchaeological data with account books from castles in Kastelholm (Åland Islands) and Raseborg (south-western coast of Finland) in order to understand the processing and transport of fish in the area. Fish was paid as tax by the peasants but was also fished by the castle fishermen and brought to the castles to be consumed there. Here, the preserved fish products are primarily studied through pike and cod, which represent the main economically important larger fish species in the Baltic Sea. The study reveals some differences between the castles studied and the importance of fish for the castle economy.

Effective co-management and long-term reef fish recovery from severe coral bleaching: Insights from Misali Island, PECCA, Tanzania

Misali, an uninhabited islet along the east coast of Pemba Island off the mainland Tanzanian coast, is a biodiversity hotspot and Marine Protected Area (MPA), consisting of a core non-extraction zone (NEZ) surrounded by a larger area where some artisanal fishing is allowed. Within a year of receiving official protection under a co-management agreement, the island underwent a catastrophic bleaching event in 1998, and funding and enforcement in the protected area have been inconsistent since a restructuring of management in 2006. In this study, we investigate current health of the island's fish community, and report 186 observed fish species. We estimate that, including unseen species and those outside the study area, the total species richness may be comparable to the historical baseline of 244 species; however, this represents a decline from the 270 species estimated in 2001 and the 350 species observed in 2004, after several years of successful protections. Patterns of species richness over time likely reflect changes in management effectiveness and engagement of Misali's fishing communities. Diversity of indicator (Chaetodontidae) and keystone (Scarinae) taxa were comparable to historical levels and greatest inside the NEZ, suggesting continued reef health and resilience. However, we found no other significant differences between fish communities inside and outside the NEZ, which observations indicate is poorly enforced, and the disproportionate loss of large predatory fish species may indicate overfishing. The case study of Misali suggests that a temporary reduction in fishing pressure while the island was recovering from a severe bleaching event may have had long-lasting benefits for reef health and resilience. For future management, we recommend consideration of species-specific protections, a possible re-designation of NEZ boundaries to include more unique habitat types, and reintegration of local fishing communities into MPA co-management.

Individual differences exceed species differences in the movements of a river fish community

AbstractRepeatable individual differences often account for large proportions of intraspecific variation in animal movements. However, meta-population models have continued to rely on single species-level and season-specific species-level means for movement prediction. Here, we test the hypothesis that repeatable individual differences can account for a similar proportion of movement distance variation as species differences. We used radio telemetry to generate repeated measures of movement from 504 hetero-specific fish. We tracked 5 large bodied fish species (Salvelinus confluentus, Oncorhynchus mykiss, Prosopium williamsoni, Thymallus arcticus, and Sander vitreus) in the upper reaches of the Peace River, British Columbia, Canada, over 8 years. We applied a hierarchical framework to partition repeatability of movement distances at the intra- and interspecific biological levels, and among short-term (within-season) and long-term (across seasons and years) temporal levels. Our results show that long-term movement distance repeatability was higher at the intraspecific level than at the interspecific level, demonstrating that animal personality can account for more variation in movement than species differences. These findings provide a novel, community level demonstration of the importance of individual variation, highlighting the predictive gains associated with a shift in the focus of spatial ecology, away from species mean and seasonal species-level mean predictive approaches, towards a spatial behavioral types-based predictive approach.

Spatial patterns and drivers of fish and benthic reef communities at São Tomé Island, Tropical Eastern Atlantic

AbstractMarine communities vary across spatial scales due to changes in habitat structure, wave exposure, depth and anthropogenic activities. Here, we quantitatively characterized, for the first time, the reef fish assemblages and benthic communities in six sites around São Tomé Island, in the Tropical Eastern Atlantic region. We performed 139 underwater visual census and 112 photo‐quadrats across six sites around the island to explore the relative importance of exposure, depth and topographic complexity as drivers of fish and benthic reef communities. Planktivores were the most important trophic group, in terms of both fish abundance and biomass. Small fishes (0–7 cm) dominated the abundance, whereas biomass was mainly concentrated in 8–15 and 16–30 cm body size classes. About 30% of the total benthic cover was composed of turf algae and circa of 28% of calcareous coralline algae, whereas corals were comparably less abundant (only 8%). Among these, Montastraea cavernosawas the most abundant coral (46% of the coral cover and 4% of total benthic cover). Wave exposure was the most important driver of the reef fish assemblages and was also important for benthic communities. Also, fish species composition seemed to respond, although weakly, to benthic composition. Topographic complexity had little effect on the indicators of fish assemblages but seemed to drive some changes in benthic cover. Overall, our results evidence the dominance of small planktivorous reef fish assemblages and of turf algal communities in São Tomé. Taken together, they support the idea of benthic communities shaped by wave action, with minor importance of corals, and of important energetic contribution from planktonic material. We also suggest that the relatively low biomass of medium and large fish species reflects the long‐term fishing pressure in São Tomé Island.

Ecotourism impacts on the behaviour of whale sharks: an experimental approach

AbstractTourists approaching wild animals can potentially cause disturbance as a result of the perceived predation risk. Risk effects arise when prey alter their behaviour in response to predators. This response may carry costs through its impact on fitness-related activities such as foraging. We recorded behavioural responses of whale sharksRhincodon typusto experimental vessel and swimmer approaches. We simulated the disturbance caused by ecotourism in the foraging site of this planktivorous fish in Bahia de Los Angeles, Gulf of Baja California, Mexico. Stress-related behaviours (vigilance, change of direction, diving and acceleration) were more common directly after both types of disturbance than before, in particular after approach by a swimmer. Individuals were more likely to be vigilant when they were new to the bay, but we did not find evidence of within-season behavioural habituation. Sharks were 24% more likely to forage before human stimuli than after. Our study highlights negative effects of vessel and swimmer approaches on whale shark behaviour, with a short-term increase in stress-related behaviours potentially carrying energetic costs, combined with a decrease in food intake following the disturbance. Our results indicate concerns about the impact of ecotourism on large fish species. An important next step would be to determine whether these short-term behavioural responses to the perception of predation risk negatively affect fitness. Among other guidelines, we recommend preventing swimmers from approaching if whale sharks stop feeding when a vessel approaches.

Adipogenesis in fish.

White adipose tissue (AT) is the main lipid storage depot in vertebrates. Initially considered to be a simple lipid store, AT has recently been recognized as playing a role as an endocrine organ that is implicated in processes such as energy homeostasis and as a rich source of stem cells. Interest in adipogenesis has increased not only because of the prevalence of obesity, metabolic syndrome and type 2 diabetes in humans, but also in aquaculture because of the excessive fat deposition experienced in some cultured fish species, which may compromise both their welfare and their final product quality. Adipocyte development is well conserved among vertebrates, and this conservation has facilitated the rapid characterization of several adipogenesis models in fish. This Review presents the main findings of adipogenesis research based in primary cultures of the preadipocytes of farmed fish species. Zebrafish has emerged as an excellent model for studying the early stages of adipocyte fish development in vivo Nevertheless, larger fish species are more suitable for the isolation of preadipocytes from visceral AT and for studies in which preadipocytes are differentiated in vitro to form mature adipocytes. Differentiated adipocytes contain lipid droplets and express adipocyte marker genes such as those encoding the peroxisome proliferator activated receptor γ (pparγ), CCAAT-enhancer-binding protein α (c/ebpα), lipoprotein lipase (lpl), fatty acid synthase (fas), fatty acid binding protein 11 (fabp11), fatty acid transporter protein1 (fatp1), adiponectin and leptin. Differentiated adipocytes also have elevated glycerol 3-phosphate (G3P) dehydrogenase (GPDH) activity. To better understand fish adipocyte development and regulation, different adipokines, fatty acids, growth factors and PPAR agonists have been studied, providing relevant insights into which factors affect these processes and counterbalance AT dysregulation.

A Murray Cod assemblage: Re/considering riverScape pedagogy

ABSTRACTThis article enacts Deleuze and Guattari's (1987) concept assemblage to craft a riverScape pedagogy that is informed by, and responsive to, the Murray Cod, the river, and its circumstances. The Murray Cod, the largest fish species in Australia's Murray-Darling Basin, has diverse cultural meanings. Cod are at once a creation being of Indigenous people, a migratory predator that breeds in response to warm floodwaters, and a fish suffering significant ecological decline as a result of changes to land and water use in its habitat. Murray Cod assemblage weaves these elements together to re/create a bioegalitarian pedagogy, part thought experiment and part teaching strategy.

Phenology of three coexisting annual fish species: seasonal patterns in hatching dates

Annual fish are specialized freshwater fishes that are adapted to live in seasonal freshwater pools. Their life cycle is tightly adapted to seasonally predictable aquatic and desiccated phases in their habitat. We used daily increments in otoliths to test the hypothesis of the direct association between seasonal rains and hatching dates of three coexisting Austrolebias species across 14 temporary pools in the Uruguayan pampa. Hatching was relatively synchronous within and between species across a small but topographically diverse region. Hatching occurred over 1 month in midautumn and peaked between 15 and 20 April 2015. The prediction of earlier hatching of a large predatory annual fish species was not confirmed. Unexpectedly, an unusual desiccation event in the middle of the winter growing season (May–July) affected many pools. Some pools re-filled after extensive precipitation in August, followed by the hatching of a new cohort in some (but not all) of those pools. The first cohort survived throughout the year (until late spring) in the pools that did not desiccate. Our study demonstrates how annual fish can cope with unexpected seasonal rainfall patterns that may be a consequence of current climate change.

Deep pelagic food web structure as revealed by in situ feeding observations.

Food web linkages, or the feeding relationships between species inhabiting a shared ecosystem, are an ecological lens through which ecosystem structure and function can be assessed, and thus are fundamental to informing sustainable resource management. Empirical feeding datasets have traditionally been painstakingly generated from stomach content analysis, direct observations and from biochemical trophic markers (stable isotopes, fatty acids, molecular tools). Each approach carries inherent biases and limitations, as well as advantages. Here, using 27 years (1991–2016) of in situ feeding observations collected by remotely operated vehicles (ROVs), we quantitatively characterize the deep pelagic food web of central California within the California Current, complementing existing studies of diet and trophic interactions with a unique perspective. Seven hundred and forty-three independent feeding events were observed with ROVs from near-surface waters down to depths approaching 4000 m, involving an assemblage of 84 different predators and 82 different prey types, for a total of 242 unique feeding relationships. The greatest diversity of prey was consumed by narcomedusae, followed by physonect siphonophores, ctenophores and cephalopods. We highlight key interactions within the poorly understood ‘jelly web’, showing the importance of medusae, ctenophores and siphonophores as key predators, whose ecological significance is comparable to large fish and squid species within the central California deep pelagic food web. Gelatinous predators are often thought to comprise relatively inefficient trophic pathways within marine communities, but we build upon previous findings to document their substantial and integral roles in deep pelagic food webs.

Fishing‐down within populations harms seed dispersal mutualism

AbstractLarge fish are often the most effective seed dispersers, but they are also the preferred target for fisheries. We recently started to comprehend the detrimental impacts of the extirpation of large frugivorous fish species on natural forest regeneration, but we lack a general understanding of how intraspecific size‐selective harvest affects fish–fruit mutualism. Our literature review demonstrated that large individuals within populations positively affect diverse aspects of seed dispersal, from consuming a higher diversity of seeds to enhancing germination. Furthermore, we filled a research gap by studying how individual size variations within two small frugivorous fish species (<16 cm) affect seed dispersal in flooded savannas. Even within small‐bodied species, large individuals swallow a higher number of intact seeds, but not necessarily a higher proportion. Overall, our results demonstrate the disproportional role of large‐bodied individuals as key seed dispersers in flooded habitats. Consequently, fishing‐down within both large‐ and small‐bodied species can negatively affect seed dispersal and natural regeneration in overfished wetlands.

A large predatory reef fish species moderates feeding and activity patterns in response to seasonal and latitudinal temperature variation

Climate-driven increases in ocean temperatures are expected to affect the metabolic requirements of marine species substantially. To mitigate the impacts of increasing temperatures in the short-term, it may be necessary for ectothermic organisms to alter their foraging behaviour and activity. Herein, we investigate seasonal variation in foraging behaviour and activity of latitudinally distinct populations of a large coral reef predator, the common coral trout, Plectropomus leopardus, from the Great Barrier Reef, Australia. P. leopardus exhibited increased foraging frequency in summer versus winter time, irrespective of latitude, however, foraging frequency substantially declined at water temperatures >30 °C. Foraging frequency also decreased with body size but there was no interaction with temperature. Activity patterns were directly correlated with water temperature; during summer, the low-latitude population of P. leopardus spent up to 62% of their time inactive, compared with 43% for the high-latitude population. The impact of water temperature on activity patterns was greatest for larger individuals. These results show that P. leopardus moderate their foraging behaviour and activity according to changes in ambient temperatures. It seems likely that increasing ocean temperatures may impose significant constraints on the capacity of large-bodied fishes to obtain sufficient prey resources while simultaneously conserving energy.

Homestead pond polyculture can improve access to nutritious small fish

In Bangladesh, homestead pond aquaculture currently comprises a polyculture of large fish species but provides an ideal environment to integrate a range of small fish species. Small fish consumed whole, with bones, head and eyes, are rich in micronutrients and are an integral part of diets, particularly for the poor. Results from three large projects demonstrate that the small fish, mola (Amblypharyngodon mola) contributes significantly to the micronutrients produced from all fish, in homestead ponds, in one production cycle. Mola contributed 98%, 56% and 35% of the total vitamin A, iron and zinc produced, respectively, despite comprising only 15% of the total fish production by weight. If consumed within the household, mola could contribute half of the vitamin A and a quarter of the iron intake recommended for a family of four, annually. Homestead ponds are uniquely accessible to women who prepare the household food. Further dissemination of the carp-small fish technology provides opportunities to target women and men together for training on fish production and consumption, nutrition and gender equity. Women only training is also recommended to enable them to engage fully, without feeling dominated by men. Partnering with the fisheries and health sectors will encourage sustainable uptake of this promising technology. Clearly, dissemination could have significant health benefits; however, improved monitoring and evaluation, particularly of dietary diversity and diet quality are essential. Research priorities should also include the production techniques of other small indigenous fish species (SIS), besides mola, and the power dynamics between women and men in operating homestead ponds.

Coherent assessments of Europe’s marine fishes show regional divergence and megafauna loss

Europe has a long tradition of exploiting marine fishes and is promoting marine economic activity through its Blue Growth strategy. This increase in anthropogenic pressure, along with climate change, threatens the biodiversity of fishes and food security. Here, we examine the conservation status of 1,020 species of European marine fishes and identify factors that contribute to their extinction risk. Large fish species (greater than 1.5 m total length) are most at risk; half of these are threatened with extinction, predominantly sharks, rays and sturgeons. This analysis was based on the latest International Union for Conservation of Nature (IUCN) European regional Red List of marine fishes, which was coherent with assessments of the status of fish stocks carried out independently by fisheries management agencies: no species classified by IUCN as threatened were considered sustainable by these agencies. A remarkable geographic divergence in stock status was also evident: in northern Europe, most stocks were not overfished, whereas in the Mediterranean Sea, almost all stocks were overfished. As Europe proceeds with its sustainable Blue Growth agenda, two main issues stand out as needing priority actions in relation to its marine fishes: the conservation of marine fish megafauna and the sustainability of Mediterranean fish stocks. Assessing the conservation status of 1,020 European marine fishes reveals half of large (>1.5 m) fishes are threatened with extinction and stock status diverges geographically: almost all Mediterranean stock is overfished, most northern European stock is not.

Acoustically monitoring the Hawai‘i longline fishery for interactions with false killer whales

False killer whales (Pseudorca crassidens) feed primarily on several species of large pelagic fish, species that are also targeted by the Hawai‘i-permitted commercial deep-set longline fishery. False killer whales have been known to approach fishing lines in an attempt to procure bait or catch from the lines, a behavior known as depredation. This behavior can lead to the hooking or entanglement of an animal, which currently exceeds sustainable levels for pelagic false killer whales in Hawai‘i. Passive acoustic monitoring (PAM) was used to record false killer whales near longline fishing gear to investigate the timing, rate, and spatial extent of false killer whale occurrence. Acoustic data were collected using small autonomous recorders modified for deployment on the mainline of longline fishing gear. A total of 90 fishing sets were acoustically monitored in 2013 and 2014 on a chartered longline vessel using up to five acoustic recorders deployed throughout the fishing gear. Of the 102 odontocete click and/or whistle bouts detected on 55 sets, 26 bouts detected on 19 different fishing sets were classified as false killer whales with high or medium confidence based on either whistle classification, click classification, or both. The timing of false killer whale acoustic presence near the gear was related to the timing of fishing activities, with 57% of the false killer whale bouts occurring while gear was being hauled, with 50% of those bouts occurring during the first third of the haul. During three fishing sets, false killer whales were detected on more than one recorder, and in all cases the whales were recorded on instruments farther from the fishing vessel as the haul proceeded. Only three of the 19 sets with acoustically-confirmed false killer whale presence showed signs of bait or catch damage by marine mammals, which may relate to the difficulty of reporting depredation. PAM has proven to be a relatively inexpensive and efficient method for monitoring the Hawai‘i longline fishery for interactions with false killer whales.

Long-term satellite tracking reveals variable seasonal migration strategies of basking sharks in the north-east Atlantic

Animal migration is ubiquitous in nature with individuals within a population often exhibiting varying movement strategies. The basking shark (Cetorhinus maximus) is the world’s second largest fish species, however, a comprehensive understanding of their long-term wider-ranging movements in the north-east Atlantic is currently lacking. Seventy satellite tags were deployed on basking sharks over four years (2012–2015) off the west coast of Scotland and the Isle of Man. Data from 28 satellite tags with attachment durations of over 165 days reveal post-summer ranging behaviours. Tagged sharks moved a median minimum straight-line distance of 3,633 km; achieving median displacement of 1,057 km from tagging locations. Tagged individuals exhibited one of three migration behaviours: remaining in waters of UK, Ireland and the Faroe Islands; migrating south to the Bay of Biscay or moving further south to waters off the Iberian Peninsula, and North Africa. Sharks used both continental shelf areas and oceanic habitats, primarily in the upper 50–200 m of the water column, spanning nine geo-political zones and the High Seas, demonstrating the need for multi-national cooperation in the management of this species across its range.

Invasive species alter ontogenetic shifts in the trophic ecology of Lake Sturgeon (Acipenser fulvescens) in the Niagara River and Lake Ontario

Species invasions can alter food web structure and change ecosystem-level functioning, but it is often unclear how these invasions may affect the life history of native species. The Lake Sturgeon (Acipenser fulvescens), a large long-lived native fish species in the Great Lakes, has increased in abundance in the lower Niagara River and nearby Lake Ontario during a period of invasive species-induced ecosystem change precipitated most recently by Dreissenid mussels (Driessena polymorpha and Driessena bugensis) and Round Goby (Neogobius melanostomus). Material taken from cross-sections of archived pectoral spines from Niagara River Lake Sturgeon captured in 1998–2000 and 2010–2012 were analyzed for stable isotopes across discrete growth zones to provide an ontogenetic assessment of diet, and diet analysis of Lake Sturgeon captured in 2014 was conducted to assess the contribution of invasive prey. Round Goby was the most important Lake Sturgeon prey item (86% by weight) in 2014, which corroborated results of δ15N and δ13C. Lake Sturgeon captured after the invasion of Round Goby exhibited ontogenetic changes in δ15N that differed from pre-Round Goby patterns, though this effect was weaker for δ13C. Values of δ15N from spine growth zones indicated non-linear increases in trophic position with age and increased rate of δ15N enrichment after the Round Goby invasion. We conclude that Round Goby establishment in western Lake Ontario changed the feeding ecology of Lake Sturgeon, which may have a positive effect on population growth for this native species.

Surveillance of Total Mercury and Methylmercury Concentrations in Retail Fish.

Most fish samples contain methylmercury, that the concentrations very greatly according to the fish species. To avoid the adverse health effects of methylmercury while retaining the benefits provided by fish consumption, it is important to select suitable fish species and to control the amount of the fish intake. We surveyed the concentrations of total mercury and methylmercury in 210 retail fish samples classified into 19 fish species by using validated analytical methods. The results of this survey were as follows. The total mercury and methylmercury concentrations were higher than 1 mg/kg in some samples of swordfish and bluefin tuna, which are large predatory fish species. In bluefin tuna and yellowtail, total mercury and methylmercury concentrations in farm-raised fish were lower than those in natural fish. There was a positive correlation between total mercury concentration and methylmercury concentration. Our results indicate that a cut-off value of 0.3 mg/kg total mercury in the screening of fish samples would increase the effectiveness of inspection.

Disentangling seafood value chains: Tourism and the local market driving small-scale fisheries

Identifying socio-economic drivers of small-scale fisheries is a fundamental step to understand impacts and pressures on fishery resources, and the behaviour of seafood trade actors. It is especially relevant for developing countries where such information is usually lacking and fisheries management is greatly needed. To address this gap, this study maps the structure of value chains of fish and marine invertebrates caught by small-scale fisheries from São Vicente, Cape Verde (West Africa), and examines the main socio-economic drivers behind the seafood trade on the island. Specifically, it shows how drivers, such as tourism and the local market, shape the preferences for certain species and how they affect the distribution of income among actors involved in the seafood trade. To collect this information, interviews were done with fishers, small-scale traders, market vendors, and restaurant owners, in all fishing communities of the island of São Vicente, in 2015. Tourism and the local market drive the exploitation of a wide variety of marine species, from small demersal low trophic level fish and marine invertebrates, to large pelagic high trophic level fish species. Moreover, the local seafood market, and especially tourism dynamics, contribute to the unequal distribution of income among actor groups, benefiting mostly restaurant owners due to their direct access to tourist consumers. Such findings have implications for local fishery resources management, food security, and fishing communities’ livelihoods.

Isolation-by-time population structure in potamodromous Dourado Salminus brasiliensis in southern Brazil

Isolation-by-distance is recognized as a useful model for describing the spatial distribution of gene frequencies depending on dispersal characteristics of the species under study. However, some species may have populations that occupy the same geographic distribution during the breeding season yet reproduce at different time periods resulting in isolation-by-time (IBT). IBT may complicate investigations of spatial population structure if samples are obtained from multiple discrete time periods or may remain undiscovered if surveys are conducted with limited temporal scope. IBT has been observed in several studies of anadromous fishes (primarily salmon) as well as a few examples in taxa such as frogs, plants, birds and insects, but has not been rigorously tested in freshwater fishes. In this study, we assessed spatial and temporal genetic variation and tested for IBT in Dourado (Salminus brasiliensis), a large and commercially-important potamodromous fish species found in multiple river basins of South America. Using 11 polymorphic microsatellite loci, we estimated genetic differentiation of 317 adult Dourado collected monthly during the breeding season at three locations along the Uruguay River in southern Brazil. Analyses identified three populations that were clustered in time (i.e. early, middle and late), suggesting an IBT pattern of population structure with no significant spatial structure. Our results contribute to the mounting evidence across a wide range of taxa that suggests IBT may be more common that currently considered, even for species with very high dispersal capabilities such as potamodromous fishes.

Maximum swimming speeds of sailfish and three other large marine predatory fish species based on muscle contraction time and stride length: a myth revisited.

ABSTRACTBillfishes are considered to be among the fastest swimmers in the oceans. Previous studies have estimated maximum speed of sailfish and black marlin at around 35 m s−1 but theoretical work on cavitation predicts that such extreme speed is unlikely. Here we investigated maximum speed of sailfish, and three other large marine pelagic predatory fish species, by measuring the twitch contraction time of anaerobic swimming muscle. The highest estimated maximum swimming speeds were found in sailfish (8.3±1.4 m s−1), followed by barracuda (6.2±1.0 m s−1), little tunny (5.6±0.2 m s−1) and dorado (4.0±0.9 m s−1); although size-corrected performance was highest in little tunny and lowest in sailfish. Contrary to previously reported estimates, our results suggest that sailfish are incapable of exceeding swimming speeds of 10-15 m s−1, which corresponds to the speed at which cavitation is predicted to occur, with destructive consequences for fin tissues.