Young-of-the-year Abundance Research Articles

Is recruitment of brown trout in a New Zealand river driven by parental spawning investment, density dependence, or environmental factors?

This study addresses the primary factors driving young-of-the-year (YoY) brown trout Salmo trutta abundance and population dynamics through the Austral summer in an important spawning tributary of a large New Zealand river. We measured the key traits and spawning investment of spawners; YoY density and movement; and environmental characteristics important for juvenile trout. In comparison to their native European range, we found high rates of pre-spawning mortality, low density of deposited eggs and reduced spawning efficiency of adult brown trout. Parental spawning investment did not affect spring juvenile trout distribution, a result likely related to a mismatch between YoY abundance and densities of eggs deposited by adults at the sampled locations. Spatial differences in seasonal dynamics of YoY density were likely related to the diversity of environmental conditions affecting habitat suitability for post-larval brown trout along the stream. Significant correlations between juvenile trout loss rate and both YoY density and downstream migration were observed only for the lowland stream segments, which had the highest spawning investment from diadromous adults, indicating the importance of these locations for recruitment. This study highlights knowledge gaps in species-environment interactions and the reproductive ecology of brown trout in New Zealand.

Sciaenid courtship sounds correlate with juvenile appearance and abundance in the May River, South Carolina, USA

Black drum Pogonias cromis, red drum Sciaenops ocellatus, silver perch Bairdiella chrysoura, and spotted seatrout Cynoscion nebulosus belong to the family Sciaenidae and are commonly found in South Carolina (USA) estuaries. Fish within this family produce sounds that are associated with courtship behavior and spawning. By listening to estuarine soundscapes, we can identify spawning aggregations. In this study, our objectives were to investigate long-term patterns of black drum, silver perch, spotted seatrout, and red drum calling and chorusing (i.e. indicative of spawning) over a 6 yr time span; identify any shifts in seasonal sound production from one year to the next; and examine the relationship between chorusing and young-of-the-year (YOY) abundance collected through haul seines. We found that in years with warmer springs, black drum, silver perch, and spotted seatrout began chorusing earlier and had longer chorusing seasons than in the years with cooler temperatures. Inversely, cooler temperatures during late summer led to earlier and longer spawning seasons for red drum. We detected the appearance of YOY in the estuary approximately 1 mo after initiation of the chorusing season. Silver perch were the most abundant in the spring, spotted seatrout during the summer, and red drum during the fall. Additionally, we found positive correlations between chorusing and YOY abundance. In years with longer chorusing seasons, we detected higher abundance of silver perch, spotted seatrout, and red drum YOY than in the years with shorter chorusing periods. These patterns provide supporting evidence that passive acoustics can aid inmonitoring reproductive output of an estuary.

Recruitment dynamics of non-native largemouth bass within the Sacramento–San Joaquin Delta

Largemouth bass (LMB; Micropterus salmoides) recruitment is limited by a critical developmental period during early life stages, but this mechanism may be less important within non-native habitats. We conducted boat electrofishing surveys in four tidal lakes of California’s Sacramento–San Joaquin Delta (SSJD) from 2010 to 2011 to describe introduced LMB recruitment dynamics. We evaluated growth, proximate composition, and health indices of young-of-the-year (YOY) LMB among tidal lakes and developed an integrated count model to determine how factors known to affect LMB recruitment shape SSJD population structure. Our results show a mismatch among growth, nutrition, and YOY abundance, where the tidal lake with the most abundant and fastest-growing LMB had the poorest nutritional status. The warm winter water temperatures and lack of a hatching-cohort growth advantage suggests overwinter starvation plays a less important role in SSJD LMB recruitment than in many native LMB habitats. Collectively, our results suggest that habitat characteristics (submerged aquatic vegetation) and not overwinter mortality shapes SSJD LMB population structure, a mechanism consistent with contemporary hypotheses about the altered fish community structure of the SSJD.

Native brook trout and invasive rainbow trout respond differently to seasonal weather variation: Spawning timing matters

Abstract Salmonids have been introduced globally, and native and invasive salmonids co‐exist in many regions. However, their responses to seasonal weather variation and global climate change are poorly known. The aim of this study was to compare effects of inter‐annual variation in seasonal weather patterns on native brook trout (BKT) (Salvelinus fontinalis) versus invasive rainbow trout (RBT) (Oncorhynchus mykiss) abundance using summer electrofishing data (May through September) spanning 28 years in the Great Smoky Mountains National Park, U.S.A. (c. 200 stream sites per species). In particular, we tested if different spawning timing between BKT (autumn) and RBT (late winter) would result in heterogeneous population responses to high seasonal precipitation, which would negatively affect early life stages with impaired swimming ability. As predicted, young‐of‐the‐year (YOY) abundance of autumn‐spawning BKT was most strongly impacted by total precipitation between February and March, and RBT YOY abundance was most strongly impacted by peak precipitation between April and May. Despite the presence of these different key seasonal drivers, inter‐annual variation in YOY density of these two species was positively correlated because precipitation in April and May also impacted the abundance of BKT YOY. Adult abundance was less responsive to weather variation than YOY abundance, and was most strongly correlated with YOY abundance in the previous year, indicating the importance of flow‐driven population control influences on early life stages affecting population sizes into subsequent years. Adult BKT densities were not affected by any weather covariate, whereas adult RBT densities were correlated with four weather covariates in competing models. As a result, there was no correlation in the inter‐annual variation in adult density in these two species. The differing responses of BKT and RBT to long‐term seasonal weather patterns suggest that they will likely respond differently to global climate change. In particular, winter precipitation will likely be the key environmental driver of differences in their population responses.

Seasonal temperature and precipitation regulate brook trout young‐of‐the‐year abundance and population dynamics

Summary Abundance of the young‐of‐the‐year (YOY) fish can vary greatly among years and it may be driven by several key biological processes (i.e. adult spawning, egg survival and fry survival) that span several months. However, the relative influence of seasonal weather patterns on YOY abundance is poorly understood. We assessed the importance of seasonal air temperature (a surrogate for stream temperature) and precipitation (a surrogate for stream flow) on brook trout (Salvelinus fontinalis) YOY summer abundance using a 29‐year data set from 115 sites in Shenandoah National Park, Virginia, U.S.A. We used a Bayesian hierarchical model that allowed the effect of seasonal weather covariates to vary among sites and accounted for imperfect detection of individuals. Summer YOY abundance was affected by preceding seasonal air temperature and precipitation, and these regional‐scale drivers led to spatial synchrony in YOY abundance dynamics across the 170‐km‐long study area. Mean winter precipitation had the greatest effect on YOY abundance and the relationship was negative. Mean autumn precipitation, and winter and spring temperature had significantly positive effects on YOY abundance, and mean autumn temperature had a significant negative effect. In addition, the effect of summer precipitation differed along a latitudinal gradient, with YOY abundance at more northern sites being more responsive to inter‐annual variation in summer precipitation. Strong YOY years resulted in high abundance of adults (>age 1 + fish) in the subsequent year at more than half of sites. However, higher adult abundance did not result in higher YOY abundance in the subsequent year at any of the study sites (i.e. no positive stock–recruitment relationship). Our results indicate that YOY abundance is a key driver of brook trout population dynamics that is mediated by seasonal weather patterns. A reliable assessment of climate change impacts on brook trout needs to account for how alternations in seasonal weather patterns impact YOY abundance and how such relationships may differ across the range of brook trout distribution.

Effect of environmental conditions on juvenile recruitment of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) in fresh water: a coastwide perspective

The abundance of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) has declined throughout their range, and there are increasing concerns about their conservation status. Because of their diadromous life history, variability in rates of survival in fresh water can affect overall recruitment. The objective of our study was to assess how river temperature and flow influence young of the year (YOY) river herring recruitment in the Northeast US. Observations of adult and juvenile fish in five rivers were used to construct spawner–YOY recruits models; these rivers were chosen because of the length of the time series (>15 years) and the paired observations of spawners and juveniles. An environmentally explicit stock–recruitment model explained a substantial fraction (41% to 80%) of the variance in YOY abundance, depending on river system. Our approach allowed for a preliminary discussion of potential mechanisms, which need to be further substantiated by focused field and laboratory studies. Early summer river flow and river temperature had the greatest influence, indicating the importance of conditions in nursery habitats. In certain systems, spring or fall conditions were also important determinants of survival, suggesting additional effects of the environment on spawning of adults and juvenile egress from freshwater nursery habitats.

Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish

Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes. After a partial winterkill, we observed a reduction of fish biomass by 16 and 43% in a clear-water and a turbid small temperate lake, respectively. Fish biomass and piscivore shares (5% of fish biomass) were similar in both lakes after this winterkill, but young-of-the-year (YOY) abundances were higher in the turbid lake. Top-down control by crustaceans was only partly responsible for low phytoplankton biomass at the end of May following the winterkill in both lakes. Summer phytoplankton biomass remained low in the clear-water lake despite high abundances of YOY fish (mainly roach). In contrast, the crustacean biomass of the turbid lake was reduced in summer by a high YOY abundance (sunbleak and roach), leading to a strong increase in phytoplankton biomass. The YOY abundance of fish in shallow eutrophic lakes may thus be more important for their summer phytoplankton development after winterkill than the relative abundance of piscivores.

Use of submerged aquatic vegetation by young-of-the-year gadoid fishes in Maine estuaries

Summary The protection of nursery areas as Essential Fish Habitat (EFH) has become a key element in US Federal fisheries management. Distribution and abundance by habitat for four age-0 +, young-of-the-year (YOY) gadoid fishes (Gadus morhua Linnaeus, Atlantic cod; Pollachius virens Linnaeus, pollock; Microgadus tomcod Walbaum, tomcod; and Urophcis tenuis Mitchill, white hake) were compared for three Maine estuaries (Casco Bay, Muscongus Bay and the Weskeag River) to define EFH during April–November of 2000, 2005–2009. One beam trawl sample was collected in one to three habitats in estuaries: Zostera marina (eelgrass), Laminaria vesiculosus (kelp), and sand/mud to determine if elevated habitat complexity resulted in a higher frequency of occurrence and abundance of YOY. Habitat complexity was a significant factor for defining EFH for YOY gadoids, with abundances of YOY always significantly higher in eelgrass and/or kelp than on unvegetated sand/mud. One species, Microgadus tomcod, also was significantly more abundant in Casco Bay than in the other two estuaries.

Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 446:259-273 (2012) - DOI: https://doi.org/10.3354/meps09455 Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season Joaquim Ribeiro*, Gonçalo M. Carvalho, Jorge M. S. Gonçalves, Karim Erzini Centro de Ciências do Mar (CCMAR), Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal *Email: jmnribeiro@sapo.pt ABSTRACT: Fish assemblages in seagrass and unvegetated habitats located in shallow intertidal creeks within the saltmarsh area of the Ria Formosa coastal lagoon were sampled with a Riley push net at 3 sites on a monthly basis over a 1 yr period. The objective was to test if both habitats support similar fish assemblages in terms of abundance, diversity, assemblage structure, and size distribution, and to investigate how site and season affect the assemblages. Fish assemblages associated with these habitats were significantly different in terms of diversity, abundance, and assemblage structure. Seagrass supported a larger number of species and greater diversity, while unvegetated habitat supported greater fish numbers but only of a few species. The habitats were dominated by different groups of resident species that were responsible for major differences in fish assemblage structure between habitats. Pomatoschistus microps and young-of-the-year (YOY) Atherina presbyter dominated the unvegetated habitat, while seagrass was dominated by a diverse group of species, in particular syngnathids and small labrids, revealing different habitat preferences. Site and season were determinant factors conditioning the role of habitat in structuring fish assemblages. Distance between habitats, site elevation, and the amount of marsh drained affected fish assemblages in both habitats. Seasonal fluctuations in the presence and abundance of YOY from marine migrant and resident species were responsible for comparable changes in fish assemblage structure in both habitats. Both habitats provide a distinctive nursery area for different species, while common species reveal ontogenic distributional changes between habitats, where smaller fish appear first in unvegetated creeks. KEY WORDS: Fish fauna · Coastal lagoon · Saltmarsh · Intertidal habitats · Seasonal variations · Habitat association · Ria Formosa · South Portugal Full text in pdf format PreviousNextCite this article as: Ribeiro J, Carvalho GM, Gonçalves JMS, Erzini K (2012) Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season. Mar Ecol Prog Ser 446:259-273. https://doi.org/10.3354/meps09455 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 446. Online publication date: February 02, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Cascading life-history interactions: alternative density-dependent pathways drive recruitment dynamics in a freshwater fish

Although density-dependent mechanisms in early life-history are important regulators of recruitment in many taxa, consequences of such mechanisms on other life-history stages are poorly understood. To examine interacting and cascading effects of mechanisms acting on different life-history stages, we stocked experimental ponds with fathead minnow (Pimephales promelas) at two different densities. We quantified growth and survival of the stocked fish, the eggs they produced, and the resulting offspring during their first season of life. Per-capita production and survival of eggs were inversely related to density of stocked fish; significant egg cannibalism by stocked minnows resulted in initial young-of-the-year (YOY) densities that were inversely related to adult densities. Subsequent growth and survival of YOY were then inversely related to these initial YOY densities, and survival of YOY was selective for larger fish. Because of these compensatory processes in the egg and YOY stages, treatments did not differ in YOY abundance and mean size at the end of the growing season. Because of differences in the intensity of size-selective mortality, however, variation in end-of season sizes of YOY was strongly (and inversely) related to densities of stocked fish. When mortality was severe in the egg stage (high densities of stocked fish), final YOY size distributions were more variable than when the dominant mortality was size-selective in the YOY stage (low stocked fish densities). These differences in size variation could have subsequent recruitment consequences, as overwinter survival is typically selective for YOY fish larger than a critical threshold size. Density-dependent effects on a given life stage are not independent, but will be influenced by earlier stages; alternative recruitment pathways can result when processes at earlier stages differ in magnitude or selectivity. Appreciation of these cascading effects should enhance our overall understanding of the dynamics of stage-structured populations.

Abundance, Spatial Distribution, and Mortality of Young-of-the-Year Spotted Seatrout (Cynoscion nebulosus) Along the Gulf Coast of Florida

We used fixed-station and random-station sampling data from the period 1989-97 to examine spatial and temporal patterns in the abundance and size structure of young-of-the-year (YOY) spotted seatrout, Cynoscion nebulosus, in three Florida estuaries. YOY seatrout first appeared at shallow-water (<1.5 m) seine sites in May-June in Choctawhatchee Bay (Florida Panhandle) and in April-May in Tampa Bay and Charlotte Harbor (both along the southwest Florida peninsula). Spotted seatrout were caught at deepwater (> 1.6 m) trawl stations within 1-3 mo of their initial appearance at shallow-water sites. Most spotted seatrout were caught in waters <3.7 m. Spring and summer peal's in YOY abundance, corresponding to strong influxes of newly spawned individuals, were observed only in southwest peninsula estuaries. Depending on the estuary, the occurrence of YOY spotted seatrout at shallow-water sites was associated with some combination of seagrasses, mangroves, salinity, depth, temperature, and mud. Estimates of total instantaneous mortality rates for YOY spotted seatrout in Tampa Bay were 0.027·d-1 for fixed sites and to 0.025·d-1 for randomly selected sites.

Pre- and post-settlement factors as determinants of juvenile blue crab Callinectes sapidus abundance: results from the north-central Gulf of Mexico

We estimated juvenile abundance and predation potential for young-of-the-year (YOY) blue crabs Callinectes sapidus in upper- and lower-salinity marsh and submerged aquatic vegetation (SAV) 'nursery habitats' of Mobile Bay, Alabama, USA, and surrounding waters, and combined this information with previously published post-larval abundance data from these habitats to evaluate the relative roles of pre- and post-settlement events in determining the abundance of YOY crabs. We found little evidence for a significant relationship between megalopal supply and juvenile abundance, except shortly after a few very large, episodic pulses of postlarvae. However, even after large settlement events, in less than 14 d densities of YOY crabs had declined in a density-dependent manner to prior 'background' levels. These declines in density were probably due to high predation rates that produced as much as 95% mortality on a daily basis. As many previous studies had found, greater predation risk was recorded for crabs on unvegetated substrate than for those in SAV or marsh grass. Overall, losses to predators were high at our study sites compared to those reported in similar studies along the Atlantic coast of the United States. In both years of the study (1990 and 1991), the largest numbers of juvenile crabs were found in poly- and mesohaline SAV and salt marsh habitats. In Year 1, no significant correlations were observed between either marsh stem density or SAV vegetation biomass and YOY crab abundance, although at one location in the second year there was a significant positive correlation between the number of juveniles and mid-bay stem density. No significant differences in crab size (carapace width, CW) were found among locations in either year. In comparison with other, better-studied mid-Atlantic coast estuaries in the US (e.g., the Chesapeake and Delaware bays), very large numbers of megalopae (frequently 1 to 2 orders of magnitude greater) invade the Mobile Bay system, as well as other Gulf Coast estuaries. However, YOY abundance in marsh and SAV 'nursery habitats' was of the same order of magnitude as that reported for mid-Atlantic estuaries. We conclude that although postlarval supply was very large, post-settlement loss to predators was the dominant factor influencing blue crab population dynamics in our north central Gulf of Mexico study area.

Recruitment dynamics of bluefish (Pomatomus saltatrix) from Cape Hatteras to Cape Cod, 1973–1995

Recruitment dynamics are complicated in species in which multiple cohorts of young-of-the-year (YOY) are produced each year. Each summer, two cohorts of YOY bluefish (Pomatomus saltatrix), representing fish spawned in spring and summer, recruit to Mid-Atlantic Bight estuaries, but little is known about their interannual variability, environmental forcing, and relative contributions to later life stages. We addressed these questions by examining the distribution and abundance of YOY on the continental shelf of the US east coast in autumn from 1973 through 1995. Abundance on the continental shelf increased in autumn owing to emigration from estuaries. We found clear evidence of two cohorts in autumn length-frequency distributions in most years and used this information to construct cohort-specific indices of abundance, which were then compared with relevant environmental variables. Spring-spawned fish dominated the catch in 20 of the years examined. The summer cohort dominated only in 1992. The abundance of the two cohorts was positively correlated, rejecting the hypothesis that dominance of the spring cohort is the result of cannibalism on the summer cohort. Spring cohort abundance was not correlated with either shelf warming-rate or warm-core ring streamer activity. A strong relationship was found between winds in April and May and the abundance of spring-spawned bluefish, possibly indicating that wind-driven surface flow aids the transport of larvae and/or juveniles across the shelf-slope region. 2000 International Council for the Exploration of the Sea