Abundance Of Adult Fish Research Articles

Coupling oceanic mesoscale events with catches of the Pacific sardine (Sardinops sagax) in the Gulf of California

Adult fish abundance depends on survival of early life stages, which are susceptible -among other factors- to environmental variability. Ocean mesoscale events (i.e. eddies, costal upwelling, thermal fronts, cold filaments) can be mechanisms of enrichment, concentration, retention and dispersal in marine environments with effects on survival of marine species early life stages. The Pacific sardine (Sardinops sagax) is an important fishery resource in the Gulf of California (GC), and it can rapidly respond to environmental fluctuations leading to dramatic changes in its abundance and fishery availability. This research analyzed the relationship of frequency and duration of different mesoscale processes with catches of S. sagax in the GC. Generalized additive models were applied to evaluate the effects of mesoscale events on the reproduction period, assuming they would reflect on catches several months later. The results show that eddies mostly affected the seasons with anomalous catches, where optimal duration of both types of eddies were responsible for the significantly high catches, while very high cyclonic and very low anticyclonic eddy duration led to significantly low catches. During the seasons with mean catches, high frequency of coastal upwelling and low persistence of Tropical surface sea water (TSW) northward intrusion were responsible for higher catches, while lower ones were associated to higher persistence of TSW intrusion and lower coastal upwelling frequency. A decreasing trend of coastal upwelling and filaments was detected, while the opposite occurred with TSW intrusion. These aspects should be considered in climate change scenarios because if sea surface temperature continues to increase, its implications in mesoscale processes could have consequences in the Gulf of California trophic dynamics.

Data requirements for operating model of harvest strategy for yellowfin tuna fisheries in North Maluku Waters

This Study focused on tuna handline fisheries in Morotai Island, North Maluku. Yellowfin tuna fisheries have great potential economic value. However, the high level of exploitation by small-scale fisheries in coastal waters is feared to disrupt the sustainability of tuna resources therefore, a better management approach is needed, known as a harvest strategy, based on the use of appropriate data and a strong operating model. Indonesia’s government initiated to development of the harvest strategies to manage tuna resources within Indonesia’s archipelagic waters (FMAs 713, 714, dan 715) as a priority action of the National Tuna Management Plan (NTMP). The implementation of the strategy requires adequate data and completeness of instruments. This research tried to identify the adequacy and availability of harvest strategy data and determine yellowfin resource status with LB-SPR. The case studies demonstrate the utility of scientific monitoring data to track trends in the abundance of adult fish without requiring complex stock assessment models through gap analysis. The adequate data harvest strategy was used to condition prototype operating models for testing preliminary harvest strategies through better OMs and MSE. The results showed that the adequacy of the HS data had a gap of 1.56 with an adjustable rate of 63% or not up to standard. The level of utilization of yellowfin tuna resources using the SPR method leads to overfishing.

Development of pilot empirical harvest strategies for tropical tuna in Indonesian archipelagic waters: Case studies of skipjack and yellowfin tuna

Indonesia is a member of three tuna Regional Fisheries Management Organisations (RFMOs), but currently has limited capacity to operationally manage its tuna fisheries to maximise benefits and minimise risks of overfishing. In 2014, the Government of Indonesia initiated discussions on the potential to develop formal harvest strategies for the management of tuna resources within its archipelagic waters. This article summarizes the development of potential empirical tuna harvest strategies for use in Indonesian archipelagic waters (Fisheries Management Areas 713, 714 and 715), using skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) as demonstration case studies. The outputs of area-specific components of Western Central Pacific Ocean stock assessment were used to condition prototype operating models for testing preliminary harvest strategies by management strategy evaluation. The case studies demonstrate the utility of scientific monitoring data to track trends in abundance of adult fish, without requiring complex stock assessment models. They also demonstrate the use of relatively simple, empirical harvest control rules to adjust the levels of fishing intensity of the Indonesian fleet to achieve specific management objectives for archipelagic waters in the context of wider regional management. The approach has a broad applicability to developing coastal nations with multi-gear fisheries and relatively limited data that harvest tuna, as well as participating in RFMOs for internationally managed stocks.

Decision Analysis for the Reintroduction of Bull Trout into the Lower Pend Oreille River, Washington

AbstractThe decision to reintroduce a species can be difficult owing to conflicting opinions and objectives as well as uncertainty over the outcome. Structured decision making addresses these considerations by identifying realistic fundamental objectives and building achievable management alternatives within a quantitative modeling framework. The process is driven by participation of stakeholders that represent diverse objectives, policy mandates, and opinions regarding decision alternatives. We applied structured decision making to evaluate the reintroduction of Bull Trout Salvelinus confluentus into the lower Pend Oreille River in northeastern Washington State. We engaged stakeholders from tribal, municipal, county, state, and federal agencies to specify fundamental objectives, formulate feasible reintroduction decisions, and conceptualize a modeling framework that included biological information and stakeholder assumptions. Stakeholders requested iterative decision sets to determine the optimal recipient streams and release strategies. The optimal decision—based on the fundamental objective of maximizing adult abundance at year 10—was artificial propagation of 4,500 juvenile Bull Trout coupled with translocation of 25 adult migrants to be reintroduced into a tributary and lake system (Sullivan Lake/Harvey Creek) that produced at least 18% more adult fish relative to alternatives. Sensitivity analyses were robust to the identity of the recipient stream (i.e., Sullivan Lake/Harvey Creek was always the optimal recipient stream) but suggested that maximizing the number of artificially produced juveniles released could generate a similar number of adult Bull Trout as the coupled‐release strategy. Results also suggested that ensuring fish passage at Albeni Falls Dam on the main‐stem Pend Oreille River could increase the abundance of adult fish. The process followed for this case study can be adapted to similar decisions regarding reintroduction or other translocations of fish in other systems.

Tropical seaweed beds as important habitats for juvenile fish

Seaweed beds within tropical seascapes have received little attention as potential fish habitat, despite other vegetated habitats, such as seagrass meadows and mangroves, commonly being recognised as important nurseries for numerous fish species. In addition, studies of vegetated habitats rarely investigate fish assemblages across different macrophyte communities. Therefore, the aim of the present study was to investigate the role of tropical seaweed beds as fish habitat, particularly for juvenile fish, by comparing their fish assemblages with those of closely situated seagrass beds. Fish assemblages were assessed by visual census in belt transects, where fish were identified and their length estimated, and habitat variables were estimated for each transect. The abundance of juvenile fish in seaweed beds was twice as high as that in seagrass meadows, whereas there was no difference in total, subadult or adult fish abundance. In addition, the abundance of commercially important and coral reef-associated juveniles was higher in seaweed beds, as was fish species richness. Fish assemblages differed between habitats, with siganids being more common in seagrass meadows and juvenile Labridae and Serranidae more common in seaweed beds. These results highlight that tropical seaweed beds are important juvenile fish habitats and underscore the need to widen the view of the shallow tropical seascape.

Do novel ecosystems follow predictable trajectories? Testing the trophic surge hypothesis in reservoirs using fish

AbstractHydroelectric reservoirs are novel ecosystems that provide a variety of important services. To manage these ecosystems and their fish populations effectively, we need to develop conceptual frameworks for predicting their short‐ and long‐term responses. To advance this goal, we revisited and tested the “trophic surge hypothesis, TSH.” The TSH has been widely cited in the literature, but has not been empirically tested across numerous reservoirs. The TSH suggests that fish populations should show a hump‐shaped pattern (i.e., the non‐equilibrium phase) after river impoundment. As such, we assembled 40 recruitment and 109 adult fish abundance time series from 19 species distributed across seven reservoirs from temperate and boreal regions, and applied curve fitting analyses and model selection. We found that the hump‐shaped pattern was the predominant pattern across individual time series, providing moderate support for the TSH. Fish recruitment increased substantially during reservoir filling and was followed by an increase in adult fish lagging 3–4 years behind. The non‐equilibrium phase was transient and lasted roughly eight years for recruits, whereas it could be much longer for adults. When time series were combined across regions and sites, the support for the TSH was weaker. However, we observed significant variability in the duration, timing, and magnitude of the surge across individual time series and found that the total flooded area was the most influential predictor to explain this variability. In conclusion, the TSH and related metrics can be a useful and general predictive framework to understand how fish populations may respond to impoundment. In particular, long‐term management recommendations could be short‐sighted if formulated before convincing evidence has emerged to show that the reservoir reached its new trophic equilibrium.

Do human activities influence survival and orientation abilities of larval fishes in the ocean?

The larval stages of most marine fishes spend days to weeks in the pelagic environment, where they must find food and avoid predators in order to survive. Some fish only spend part of their life history in the pelagic environment before returning to their adult habitat, for example, a coral reef. The sensory systems of larval fish develop rapidly during the first few days of their lives, and here we concentrate on the various sensory cues the fish have available to them for survival in the pelagic environment. We focus on the larvae of reef fishes because most is known about them. We also review the major threats caused by human activities that have been identified to have worldwide impact and evaluate how these threats may impact larval-fish survival and orientation abilities. Many human activities negatively affect larval-fish sensory systems or the cues the fish need to detect. Ultimately, this could lead to decreased numbers of larvae surviving to settlement, and, therefore, to decreased abundance of adult fishes. Although we focus on species wherein the larvae and adults occupy different habitats (pelagic and demersal, respectively), it is important to acknowledge that the potential anthropogenic effects we identify may also apply to larvae of species like tuna and herring, where both larvae and adults are pelagic.

Contemporary ocean warming and freshwater conditions are related to later sea age at maturity in Atlantic salmon spawning in Norwegian rivers

Atlantic salmon populations are reported to be declining throughout its range, raising major management concerns. Variation in adult fish abundance may be due to variation in survival, growth, and timing of life history decisions. Given the complex life history, utilizing highly divergent habitats, the reasons for declines may be multiple and difficult to disentangle. Using recreational angling data of two sea age groups, one-sea-winter (1SW) and two-sea-winter (2SW) fish originated from the same smolt year class, we show that sea age at maturity of the returns has increased in 59 Norwegian rivers over the cohorts 1991–2005. By means of linear mixed-effects models we found that the proportion of 1SW fish spawning in Norway has decreased concomitant with the increasing sea surface temperature experienced by the fish in autumn during their first year at sea. Furthermore, the decrease in the proportion of 1SW fish was influenced by freshwater conditions as measured by water discharge during summer months 1 year ahead of seaward migration. These results suggest that part of the variability in age at maturity can be explained by the large-scale changes occurring in the north-eastern Atlantic pelagic food web affecting postsmolt growth, and by differences in river conditions influencing presmolt growth rate and later upstream migration.

Reduced early life growth and survival in a fish in direct response to increased carbon dioxide

Adult fish seem relatively resilient to increased carbon dioxide levels, but how early-life-stage fish fare remains less clear. In a study, the estuarine fish Menidia beryllina experienced severely reduced survival and growth rates in its early life stages under levels of ocean acidification expected later this century. This suggests that ocean acidification may affect fish populations, because small changes in early-life survival can generate large fluctuations in adult-fish abundance.

Evaluating Benchmarks of Population Status for Pacific Salmon

AbstractCanada is developing an indicator approach for assessing the biological status of conservation units of Pacific salmon Oncorhynchus spp. under its Wild Salmon Policy that is based, in part, on the abundance of adult fish. Two benchmarks will be used to place populations in one of three abundance categories. The lower benchmark is proposed to be at a level that allows for a substantial buffer between it and the abundance that would result in a population's being assessed as at risk of extirpation based on quantitative criteria used by the Committee on the Status of Endangered Wildlife in Canada. Using Monte Carlo simulation, we evaluated eight candidate lower benchmarks calculated from parameters of the stock–recruit relationship against two criteria, the probability of extirpation over 100 years and the probability of recovery to spawner abundances that result in the maximum sustainable yield in one or three generations. For modeled populations of moderate size (unfished equilibrium abundances >25,000) and moderate productivity (∼four adult recruits produced per spawner at low spawner abundances), all benchmarks protected populations from extirpation when harvest restrictions were imposed at the lower benchmark. For small or unproductive populations, none of the benchmarks was adequate to prevent populations from being at risk of extirpation. However, those benchmarks that covaried with the productivity parameter of the stock–recruitment relationship performed better and are preferred to those that were derived mainly from estimates of habitat capacity.Received May 31, 2010; accepted February 4, 2011

Seasonal dynamics in population characteristics of European bitterling Rhodeus amarus in a small lowland river

The seasonal dynamics of biological traits in a population of European bitterling Rhodeus amarus from a small river in central Europe (River Kyjovka, Czech Republic) were investigated from April 2007 to March 2008. The reproductive season lasted from early April to mid-June, with a peak in late April when > 50% of females possessed ripe eggs in their ovaries. The sex ratio was female-biased, with a higher bias following the peak in reproduction, suggesting higher mortality of males than females over the reproductive period. The population was effectively annual, with a major decrease in adult fish abundance at the end of the reproductive period. Highest relative lipid content and condition factor were observed in February, both decreasing with an increase in investment into gonads. Seasonal dynamics in somatic condition, relative lipid content and gonad mass, and their comparison with other R. amarus populations, suggest that the study population allocated a disproportionally high level of resources to reproduction.

Evaluation of a Sport Fish Stocking Program in Lakes of the Southern Murray–Darling Basin, Australia

AbstractThe golden perch Macquaria ambigua is a recreationally important freshwater sport and food fish species found throughout southeastern Australia. Stocking golden perch in impoundments has been used by fisheries managers to enhance existing wild populations for over 30 years. Despite widespread stocking, the contribution of stocked fish to golden perch populations has not been investigated. We evaluated the stocking contribution by using chemically marked golden perch fingerlings introduced into three lakes in which natural recruitment is low. We surveyed the lakes to determine the contribution of the stocked fish to the lake populations and found an overall contribution of 47 ± 9% (mean ± SE) at Reedy Lake, 55 ± 9% at Kangaroo Lake, and 90 ± 5% at Lake Charm. Our results indicate that, rather than replacing wild fish, stocked fish increased the abundance of adult fish at all three lakes. The contribution of stocked fish to each population declined with increased connectedness to the Loddon River, which served as the probable source for the wild fish population. Stocking programs can substantially augment fish populations when natural recruitment is very low.

Relative Abundance, Site Fidelity, and Survival of Adult Lake Trout in Lake Michigan from 1999 to 2001: Implications for Future Restoration Strategies

AbstractWe compared the relative abundance of lake trout Salvelinus namaycush spawners in gill nets during fall 1999–2001 in Lake Michigan at 19 stocked spawning sites with that at 25 unstocked sites to evaluate how effective site‐specific stocking was in recolonizing historically important spawning reefs. The abundance of adult fish was higher at stocked onshore and offshore sites than at unstocked sites. This suggests that site‐specific stocking is more effective at establishing spawning aggregations than relying on the ability of hatchery‐reared lake trout to find spawning reefs, especially those offshore. Spawner densities were generally too low and too young at most sites to expect significant natural reproduction. However, densities were sufficiently high at some sites for reproduction to occur and therefore the lack of recruitment was attributable to other factors. Less than 3% of all spawners could have been wild fish, which indicates that little natural reproduction occurred in past years. Wounding by sea lamprey Petromyzon marinus was generally lower for Seneca Lake strain fish and highest for strains from Lake Superior. Fish captured at offshore sites in southern Lake Michigan had the lowest probability of wounding, while fish at onshore sites in northern Lake Michigan had the highest probability. The relative survival of the Seneca Lake strain was higher than that of the Lewis Lake or the Marquette strains for the older year‐classes examined. Survival differences among strains were less evident for younger year‐classes. Recaptures of coded‐wire‐tagged fish of five strains indicated that most fish returned to their stocking site or to a nearby site and that dispersal from stocking sites during spawning was about 100 km. Restoration strategies should rely on site‐specific stocking of lake trout strains with good survival at selected historically important offshore spawning sites to increase egg deposition and the probability of natural reproduction in Lake Michigan.

Relative Abundance, Site Fidelity, and Survival of Adult Lake Trout in Lake Michigan from 1999 to 2001: Implications for Future Restoration Strategies

We compared the relative abundance of lake trout Salvelinus namaycush spawners in gill nets during fall 1999–2001 in Lake Michigan at 19 stocked spawning sites with that at 25 unstocked sites to evaluate how effective site-specific stocking was in recolonizing historically important spawning reefs. The abundance of adult fish was higher at stocked onshore and offshore sites than at unstocked sites. This suggests that site-specific stocking is more effective at establishing spawning aggregations than relying on the ability of hatchery-reared lake trout to find spawning reefs, especially those offshore. Spawner densities were generally too low and too young at most sites to expect significant natural reproduction. However, densities were sufficiently high at some sites for reproduction to occur and therefore the lack of recruitment was attributable to other factors. Less than 3% of all spawners could have been wild fish, which indicates that little natural reproduction occurred in past years. Wounding by sea lamprey Petromyzon marinus was generally lower for Seneca Lake strain fish and highest for strains from Lake Superior. Fish captured at offshore sites in southern Lake Michigan had the lowest probability of wounding, while fish at onshore sites in northern Lake Michigan had the highest probability. The relative survival of the Seneca Lake strain was higher than that of the Lewis Lake or the Marquette strains for the older year-classes examined. Survival differences among strains were less evident for younger year-classes. Recaptures of coded-wire-tagged fish of five strains indicated that most fish returned to their stocking site or to a nearby site and that dispersal from stocking sites during spawning was about 100 km. Restoration strategies should rely on site-specific stocking of lake trout strains with good survival at selected historically important offshore spawning sites to increase egg deposition and the probability of natural reproduction in Lake Michigan.

Comparison of electrofishing and trammel netting variability for sampling native fishes

The variability in size structure and relative abundance (CPUE; number of fish ≥200 mm total length, LT, collected per hour of electrofishing or trammel netting) of three native Colorado River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and trammel nets was assessed to determine which gear was most appropriate to detect trends in relative abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. Mean CV was lowest for trammel nets for humpback chub (P = 0·004) and tended to be lower for flannelmouth sucker (P = 0·12), regardless of season or diel period. Only one bluehead sucker >200 mm was collected with electrofishing. Electrofishing and trammel netting CPUE were not related for humpback chub (r = −0·32, P = 0·43) or flannelmouth sucker (r = −0·27, P = 0·46) in samples from the same date, location and hour set. Electrofishing collected a higher proportion of smaller (<200 mm LT) humpback chub (P < 0·001), flannelmouth suckers (P < 0·001) and bluehead suckers (P < 0·001) than trammel netting, suggesting that conclusions derived from one gear may not be the same as from the other gear. This is probably because these gears fished different habitats, which are occupied by different fish life stages. To detect a 25% change in CPUE at a power of 0·9, at least 473 trammel net sets or 1918 electrofishing samples would be needed in this 8 km reach. This unattainable amount of samples for both trammel netting and electrofishing indicates that detecting annual changes in CPUE may not be practical and analysis of long‐term data or stock assessment models using mark‐recapture methods may be needed to assess trends in abundance of Colorado River native fishes, and probably other rare fishes as well.

Managed flooding as a tool for supporting natural fish reproduction in man‐made lentic water bodies

AbstractIn 2001, fish diversity and abundance were investigated in six man‐made borrow pits in the flood plain of the River Dyje (Danube basin). All borrow pits had uniform habitats without shelter, and with limited spawning and nursery areas. Spawning and nursery habitat conditions in three borrow pits were experimentally improved by managed flooding during spring and summer, while the other three borrow pits were not flooded. Adult (>1 year) fish were surveyed in spring and autumn by beach seining and 0+ fish were monitored monthly by dipnetting and fry beach seine nets. Flooded borrow pits had slightly higher adult species richness, considerably higher adult fish abundance and considerably higher 0+ fish species richness and abundance. The seasonal decline in 0+ fish abundance varied between flooded and non‐flooded borrow pits, with a faster decline in 0+ abundance at non‐flooded sites. Management implications for floodplain lentic water bodies are discussed.

Offshore spawning and year-class strength of northern cod (2J3KL) during the fishing moratorium, 1994-1996

Two new surveys have been conducted in recent years to assess the status of the northern cod (Gadus morhua) stock (2J3KL). An offshore acoustic survey in spring sampled concentrations of spawning adults and estimated potential fecundity. A pelagic juvenile fish survey carried out in late summer measured cod year-class strength prior to settlement. Spawning biomass of offshore cod decreased from 11 700 t in 1994 to 2000 t in 1995 to 900 t in 1996 with a corresponding decrease in eggs spawned. This decline was mirrored in the distribution and abundance of pelagic juvenile cod. Natural mortality estimated between the egg and pelagic juvenile stages increased from –0.068·day–1 in 1994 to –0.084·day–1 in 1995 to –0.112·day–1 in 1996. The decline in year-class strength of cod appeared to result primarily from a reduction in the number of offshore spawners compounded by an increase in natural mortality during the egg and larval stages. The decline in spawners occurred 2 years after the implementation of a fishing moratorium and cannot be linked to fishing. The rapid decline in abundance of adult fish combined with increased natural mortality during the egg and larval drift is consistent with depensation.

日本近海におけるブリ漁況に関する研究 ＩＶ 日本近海におけるブリ来遊量の長期変動

We analyzed yearly changes in catches of the yellowtail Seriola quinqueradiata in set net fisheries in the adjacent waters of Japan and obtained the following results. 1) Long-term trends in fish catches show different patterns between growth stages. 2) The abundance of adult fish migrating into coastal areas of Japan has been decreasing since the 1950's, sharply in the northern (lower water temperature) regions and gradually in the southern (higher water temperature) regions. 3) However, young fish migrating into the waters of Japan has not been decreasing con-tinuously since the 1950's, and especially those migrating into southern coastal areas of Japan have increased since the mid-1970's. From these results, we conclude that the distributional/migrational range of adult fish has been reduced and restricted to southern regions, due to a decrease in its stock size, and that the distributional range of young fish has also shifted toward the southern regions.