Young-of-the-year Research Articles

Maternal provisioning gives young-of-the-year Hammerheads a head start in early life

For species that do not provide parental care after birth, excess maternal provisioning during development, beyond what is required for embryogenesis, provides offspring with resources to increase their chances of survival. Maternally derived resources are expected to be important for buffering offspring against limited food resources at birth or time needed to learn how to properly feed. Young-of-the-year (YOY) cryptic Scalloped Hammerheads (Sphyrna lewini) and Carolina Hammerheads (Sphyrna gilberti) were sampled from nurseries along the US Atlantic Coast and compared for a number of biological condition metrics across three developmental stages. Large declines in liver lipid content and hepatosomatic indices were found in neonatal sharks, using umbilical scar healing as a proxy for time since birth. Feeding commenced quickly as 96% of sharks had prey remnants in their stomachs. The combination of rapid exhaustion of maternally provided resources and high occurrence of stomachs with prey contents indicate that nursery quality, with respect to prey availability, may be important for YOY hammerhead survivorship. While externally the two species are morphologically similar, longer length-at-birth in S. lewini and higher hepatic condition in neonatal S. gilberti suggest that aspects of reproductive biology, including physiology, may differ between species. While more information is needed to distinguish life history differences between these two species, data collected from YOY may serve as a useful proxy to inform management when adult samples of cryptic species are difficult to collect.

Recruitment dynamics of a migratory fish in a semiarid river system

ABSTRACT Recruitment dynamics of Neotropical migratory fishes are widely studied in river–floodplain systems, where the flood pulse and wetlands play a central role. In semiarid systems, where the flow regime is less predictable and waterbodies are intermittent, migratory fishes may employ different recruitment strategies. We investigated factors affecting the recruitment dynamics of a migratory fish (Prochilodus hartii) in a semiarid river basin (Jequitinhonha River, Brazil) subjected to river regulation. We sampled eggs, larvae, young-of-the-year (YOY), and subadults over multiple years and at several sites distributed along 300 km of the Jequitinhonha River. Biotic variables were investigated against 13 predictors through different modeling approaches to examine (1) spawning dynamics and its relationship to the flow regime, (2) habitat features related to the presence of YOY, and (3) the relationship between recruitment and floods. Higher densities of eggs and larvae occurred at sites with no influence of river regulation, affected mainly by weekly and daily variations in water level. YOY detection increased by 40% when a lateral stream was present, and occupancy was affected by the length of the lotic stretch. Subadult abundance was not correlated with any predictor related to the flooding regime. Our results show that spawning took place at multiple sites, affected mainly by flow variations, while development and recruitment occurred mostly within river channels and in the confluence of small intermittent tributaries, with little dependence on floods. Therefore, fish recruitment in this semiarid system showed different relationships with floods when compared with river–floodplain systems, highlighting the singularity of drylands.

Evidence of post-larval growth-selective mortality in Atlantic mackerel revealed by the collection of young-of-the-year juveniles ingested by the northern gannet

The growth-survival paradigm predicts that year-class strength is determined by growth-dependent mortality during the larval stage. In Atlantic mackerel Scomber scombrus, the possibility that strong growth-dependent mortality extends into the early juvenile stage has not previously been tested because of the difficulty in sampling young-of-the-year (YOY) juveniles. The present study determined the timing of the ‘endpoint’ during the early ontogeny, when growth-selective mortality decreases and recruitment is set. We relied on regurgitations from one of the main predators of mackerel, the northern gannet Morus bassanus, as a source of YOY juveniles. Early growth trajectories of YOY mackerel were reconstructed from the otolith microstructure and were compared to those of 1-yr-old (OYO) juveniles from the same cohort for the year classes of 2015 and 2017. In both cohorts, the early growth trajectory of OYO fish was faster than that of YOY juveniles, indicating that growth-selective mortality extended beyond the larval stage. For the 2017 cohort, the comparison of larval growth trajectories between 2-mo-old YOY, 3mo-old YOY and OYO juveniles indicated that strong selection for fast growth persisted until the pre-wintering period, but that winter mortality likely did not play an important role in shaping year-class strength. These findings suggest that in Atlantic mackerel, the endpoint when the relative strength of cohorts is fixed occurs at the age of 3 mo. These results highlight the importance of considering growth-dependent mortality processes occurring beyond the larval stage to obtain a better understanding of causes of recruitment variability.

Young-of-the-Year Yellowmouth Barracuda Sphyraena viridensis (Cuvier, 1829) Growth in Eastern Algeria Based on Otolith Microstructure Analysis

Age estimates were made on otoliths of 32 young-of-the-year (YOY) Barracuda, Sphyraena viridensis Cuvier (1829), captured in the south-western Mediterranean Sea. Increments were observed in Barracuda sagittae sectioned in a transverse plane and viewed with light microscopy. Increment counts were made for age estimation. Estimated ages ranged from 27 to 299 days of fish ranging in size from 15.9 to 38.9 cm total length (TL). The observed mean growth rate is 3.487 mm.day−1. Decreasing growth performance is evidenced according to age: 3.822 mm.day−1 between 159 and 302 mm (27–139 days), 1.596 mm.day−1 between 352 and 389 mm (172–299 days).

Spatial and Temporal Influences of Nearshore Hydrography on Fish Assemblages Associated with Energy Platforms in the Northern Gulf of Mexico

In 2013–2014, remote video and diver surveys documented fish assemblages around 150 small oil platforms in nearshore federal waters off the entire Louisiana coast (≤ 18 m depth). Results were used to evaluate ecological processes driving differences in fish abundance and assemblages associated with platforms. The nearshore zone was characterized by high spatial and temporal environmental heterogeneity. Surveys documented 55 species of platform-associated fishes. Twenty-nine species were partially or wholly represented by young-of-the-year (YOY) or age 1–2 juveniles, including red, gray, and lane snapper (Lutjanus campechanus, Lutjanus griseus, and Lutjanus synagris), greater amberjack (Seriola dumerili), and gag grouper (Mycteroperca microlepis). Assemblages were compared among three coastal regions with different hydrography due to interactions between river discharge and bathymetry. Assemblage composition near platforms varied in a region × year interaction associated with inter-annual differences in river discharge and coastal distribution of Sargassum drifts. The probability of YOY L. campechanus occurrence increased with bottom DO saturation (1.40–124.3%) from 0.15 to 0.72. The probability of YOY L. synagris and M. microlepis respectively decreased and increased with depth (5.61–16.76 m) from 0.81 to 0.05 and from 0.03 to 0.68. The results show that fish assemblages around platforms in the nearshore zone experienced substantial inter-regional and inter-annual differences that were driven by hydrographic and recruitment variability. Platforms also provided suitable reef habitat for juvenile fishes in areas that experience widespread bottom water hypoxia and large freshwater inflows, highlighting the importance of nearshore platforms as nursery locations for juvenile fishes that represent a variety of early life-history strategies.

Overwintering survivorship and growth of young-of-the-year black sea bass Centropristis striata.

Overwintering conditions have long been known to affect fish survival and year-class strength as well as determine the poleward range limit of many temperate fishes. Despite this known importance, mechanisms controlling overwintering mortality are poorly understood and the tolerance of marine fishes to the combined effects of winter temperature, salinity, and size is rarely quantified. In recent years, higher abundances of the temperate Serranid, black sea bass Centropristis striata, have been observed at latitudes further north than their traditional range suggesting that warming water temperatures, particularly during winter, may be facilitating the establishment of a population at more northern latitudes. To examine overwintering survival of C. striata, the combined effects of temperature, salinity and body mass were quantified in laboratory experiments. We identified 6°C as the lower incipient lethal temperature for C. striata, below which fish cease feeding, lose weight rapidly and die within 32 days. A short cold exposure experiment indicated that temperatures below 5°C resulted in mortality events that continued even as the temperature increased slowly to 10°C, indicating that even short cold snaps can impact survival and recruitment in this species. Importantly, fish in lower salinity lived significantly longer than fish at higher salinity at both 3°C and 5°C, suggesting that osmoregulatory stress plays a role in overwintering mortality in this species. Size was not a critical factor in determining overwintering survival of young-of-the-year (YOY) C. striata. Overwintering survival of YOY C. striata can be effectively predicted as a function of temperature and salinity and their interaction with an accelerated failure model to project future range limits. Identifying temperature thresholds may be a tractable way to incorporate environmental factors into population models and stock assessment models in fishes.

After the nursery: Regional and broad‐scale movements of sharks tagged in the Caribbean

AbstractBroad‐scale movements (10s–100s km) of highly migratory species, such as sharks, present unique management challenges as fish migrate across international boundaries, thereby exposing them to different levels of anthropogenic pressure. Lemon sharks and blacktip sharks are well‐studied throughout their range in the western North Atlantic, but broad‐scale movements in the Caribbean region are largely unknown. Utilizing 10 years (2004–2014) of acoustic and conventional tagging data, this study presents the post‐nursery movements of young of the year (YOY) and juvenile blacktip (n = 198) and lemon (n = 130) sharks tagged in the United States Virgin Islands (USVI). A total of five (2.5%) blacktip sharks were recaptured by recreational and commercial fishers in the greater Caribbean and as far north as the southeastern coast of the United States, moving between 2 and 2,200 km and crossing a minimum of six international boundaries. Of the acoustically tagged blacktip (n = 88) and lemon (n = 45) sharks, 28 (32%) and 16 (24%), respectively, were detected outside the boundaries of the nursery area in which they were tagged, dispersing throughout the USVI territory; blacktip sharks were acoustically detected beyond territorial waters as far as Florida, United States (1,881 km). Both species transited through local marine protected areas but did not establish residency resulting in little protection. This is the first study to examine connectivity between blacktip shark populations of the USVI and the east coast of the United States.

Distribution and genetic variability of young-of-the-year greater amberjack (Seriola dumerili) in the East China Sea

We examined the distribution and genetic variability of the greater amberjack Seriola dumerili in the East China Sea (ECS) from the mitochondrial DNA (mtDNA) control region of young-of-the-year (YOY) individuals, which may reflect the genetic characteristics of the spawning population. In the years 2016 and 2017, a total of 165 YOY S. dumerili were collected from two different locations in the ECS: the southern part of the ECS, and western Japanese coast. The spawning period was estimated using otolith daily increments from a total of 67 larvae and juveniles collected in the ECS. Results from size and age distribution indicated that S. dumerili spawned near the shelf break region in the southern ECS from January to April. Phylogenetic analysis based on mtDNA sequence data showed no significant genetic differentiation among samples collected from different locations, implying S. dumerili in the ECS is mainly composed of one population. S. dumerili around the Japanese coast may be originated from the southern ECS.

Long-lived marine species may be resilient to environmental variability through a temporal portfolio effect.

Maintenance of genetic variation may provide resilience of populations to natural environmental variability. We used Pacific ocean perch (POP; Sebastes alutus) to test for the maintenance of adaptive variation across overlapping generations. POP are a long‐lived species characterized by widespread larval dispersal in their first year and a longevity of over 100 years. In order to understand how early marine dispersal affects POP survival and population structure, we used restriction site‐associated DNA sequencing (RADseq) to obtain 11,146 single‐nucleotide polymorphisms (SNPs) from 401 young‐of‐the‐year (YOY) POP collected during surveys conducted in 2014 (19 stations) and 2015 (4 stations) in the eastern Gulf of Alaska. Population clustering analysis showed that the POP samples represented four distinct ancestral populations mixed throughout the sampling area. Based on prior work on larval dispersal of POP, these larvae are most likely from distinct parturition locations that are mixing during their pelagic dispersal life stage. Latent factor mixed models revealed that POP larvae face significant selection during their first year at sea, which is specific to the year of their birth. Thus each adult cohort's genetic composition is heavily influenced by the environmental conditions experienced during their first year at sea. Long‐lived species relying on broadcast spawning strategies may therefore be uniquely resilient to environmental variability by maintaining a portfolio of cohort‐specific adaptive genotypes, and age truncation due to overfishing of older cohorts may have detrimental effect on the population viability.

Major biomass fluctuations in lake food webs – An example in the peri-alpine Lake Annecy

In aquatic ecosystems, young of the year (YOY) fish often exhibit strong interannual fluctuations. Because these fish prey on zooplankton and are preyed upon by piscivorous fish, strong fluctuations in their abundance may have important impacts on food web functioning. The static Ecopath model was used to assess potential impacts of strong fluctuations in YOY perch in the deep peri-alpine Lake Annecy. We modeled two contrasting years in terms of YOY perch biomass: a situation with a high biomass of YOY perch and a situation with a low biomass of YOY perch. Additionally, five models were derived from the two initial models to better explore the effects of YOY perch biomass fluctuations on food web functioning. Disparities were revealed in terms of the activity of the system (volume of flows) and the trophic transfer efficiency. When the YOY perch biomass was high, the volume of flows within the system was less important, but the trophic transfers were more efficient than when the biomass was low. The high biomass of YOY perch appeared to facilitate transfers from low to high trophic levels. The results indicated that strong variabilities in the abundance of YOY fish had little impact on the main food web flows and pathways because of the capacity of predators to feed on various prey (omnivory) but could induce significant differences in food web properties (e.g. ascendancy, robustness) and organization (e.g. cycling, mean trophic level).

Geomorphological features drive spatiotemporal dynamics of young‐of‐the‐year brown trout populations in a large New Zealand river catchment

Abstract Determining the factors driving population dynamics of stream salmonids across broad landscapes is important for understanding stream ecosystem functioning and for the management and conservation of the populations of such fish. A few studies have described the determinants of the early life history of salmonids across catchments, but none of them have examined how this spatial variation develops temporally. We hypothesised that: (1) spatiotemporal dynamics of young‐of‐the‐year (YoY) trout populations vary within the catchment, with loss rates (emigration plus mortality) being higher in lower elevation, downstream reaches than in higher elevation, upstream ones; and (2) loss rate would be density dependent, leading to reduced intra‐ and inter‐cohort competition and supporting establishment of resident populations. We tested the first hypothesis by examining relationships between geomorphic characteristics of spawning streams and temporal dynamics of YoY brown trout density, loss rate and biological traits through an austral summer across the catchment of New Zealand's fourth‐longest river, the Taieri River. To test the second hypothesis, we examined whether initial YoY density in spring and other biotic determinants affected loss rate and cohort structure dynamics, resulting in density‐dependent self‐thinning of YoY fish to avoid resource limitation. Spring YoY density and subsequent loss rate was higher in low elevation sites, corresponding to stream accessibility to migratory spawners. These significant correlations of YoY density and related biotic variables with elevation disappeared later in the season, indicating that regardless of their origin, brown trout YoY tend to form stream resident populations with multicohort structure and densities low enough to limit intraspecific competition. Our findings provide evidence that geomorphological features of the landscape affect temporal dynamics of YoY trout populations driven by density‐dependent self‐regulatory mechanisms that can control the abundance of growing fish.

Supplemental diagnosis of Gyrodactylus nebulosus Kritsky and Mizelle, 1968 (Monogenea) on 0+ age Ameiurus nebulosus (Siluriformes) considered for commercial grow-out in Southwestern Nova Scotia, Canada

Gyrodactylus nebulosus Kritsky and Mizelle, 1968 is reported for the first time from brown bullhead Ameiurus nebulosus (Siluriformes; Ictaluridae) in Nova Scotia. The study results from a screening of parasites with the potential to disrupt commercial rearing of wild-caught young-of-the-year (YOY) brown bullhead. Infected YOY were collected July 30, 2018 and estimated to be 3weeks old. Eight of 10 fish were infected. Mean intensity was 3.1 ± 3.5 with a range of 1-10. The parasite occurred all over the body surface, but particularly on the ventral regions of the head including the base of the maxillary barbels. Diagnostically important features of the anchors, ventral bar/shield, marginal hooks, and male copulatory organ are described. A partial sequence of the 18S rRNA gene (432bp) is included and represents the first confirmed molecular data for this species. Molecular analysis revealed a high similarity (99.3%) to a Gyrodactylus sp. reported from the same host, A. nebulosus, in Ontario and the next closest similarity (96.9%) to Gyrodactylus fairporti Van Cleave, 1921 from Ameiurus melas in Wisconsin. The report extends the known distribution of G. nebulosus from North Dakota, Iowa, and Ontario to Nova Scotia. The study concludes that any commercial venture to harvest local YOY brown bullhead from the wild for intense grow-out in captivity should include appropriate quarantine and therapeutic treatments for G. nebulosus as part of the operation.

Microhabitat use of landlocked juvenile Atlantic salmon (Salmo salar)

Large-scale reintroduction programs for landlocked Atlantic salmon Salmo salar are ongoing in Lakes Ontario and Champlain. Commonly, these programs involve stocking hatchery reared juveniles into streams and thus, quantifying the in situ habitat use of stocked fish can help support these efforts. To examine habitat use, we stocked young-of-the-year (YOY) Atlantic salmon into 14 reaches of the Boquet River in the Lake Champlain Basin. The habitat used by YOY Atlantic salmon, measured from microhabitats that were used versus not used, differed between early and late summer for water depth. In early summer, YOY Atlantic salmon used a more narrow range of habitats compared to late summer. However, in both early and late summer, YOY most often used intermediate values in habitat variables except for water velocity in early summer. In early summer, YOY Atlantic salmon had the highest probability of using a water depth of 26 cm, a water velocity of 1 cm/sec, and a pebble substrate. In late summer, the probability of use was highest at a water depth of 61 cm, a water velocity of 11 cm/sec, and a pebble substrate. Our results show that stocked landlocked YOY Atlantic salmon use similar habitats to anadromous populations and may help managers when determining stocking locations or habitat alterations.

Combining Harvest and Genetics to Estimate Reproduction in Wolves

ABSTRACTParameters of reproductive success are important to the management of wildlife populations. Genetic monitoring can be an effective approach for acquiring this important demographic information when traditional methods are unsuccessful, inefficient, or too expensive. This study demonstrates a novel application of genetic data opportunistically collected from harvested game to estimate a minimum annual count of breeding packs of gray wolves (Canis lupus) and to provide a coarse index of harvest vulnerability of young of the year (YOY) across packs. We used 18 microsatellite loci to genotype 98 gray wolf YOY from 2014 and 105 from 2015 harvested in Idaho, USA. Using this genotype data, we reconstructed sibling groups for each cohort using the program COLONY and treated full‐sibling litters as proxies for unique packs. In addition to evaluating our marker panel using simulations, we assessed the accuracy of empirical relationship assignments by adding YOY of known relationship from long‐term study packs to the dataset (27 individuals from 2014 and 61 from 2015) and tracking correctly reconstructed relationships. We varied COLONY input parameters to evaluate the power of relationship assignments under conditions that may be encountered when working with empirical data. We also compared COLONY's estimates of effective number of breeders based on sibship frequency to estimates based on a commonly used linkage‐disequilibrium method. All COLONY runs for both cohorts correctly identified the known sibling relationships. Among the other individuals, changes in the geographic clustering of putative siblings, probabilities of inclusion and exclusion for reconstructed sibling groups, and consistency of relationship assignments across COLONY runs suggested that marker number had a larger effect on accuracy than access to population‐level genetic data. Our estimates of breeding packs subjected to harvest within the state (52 for 2014 and 63 for 2015) differed from estimates reported by Idaho Department of Fish and Game by ≤6 for both years. Among packs that had pups harvested, most packs had 1–2 YOY harvested, whereas other packs had as many as 5 YOY harvested. All estimates of the number of effective breeders had overlapping confidence intervals regardless of method, though sibship frequency‐based estimates had larger confidence intervals than estimates using the linkage disequilibrium method. Our study shows that sibling relationships can be accurately and reliably reconstructed from harvested gray wolves, and demonstrates a valuable new use of samples collected through harvest. © 2020 The Wildlife Society.

QUANTIFYING HABITAT CONCEPTS: POPULATION IMPACTS OF STAGE-SPECIFIC SALINITY RELATIONSHIPS FOR BLACK DRUM (POGONIAS CROMIS) IN THE UPPER LAGUNA MADRE, TEXAS USA

Abstract Environmental factors can often have population effects on aquatic organisms, though studies of environmental effects are often specific to a given life stage. Stage-structured demographic models provide a means of exploring the multivariate suite of life history parameters associated with a population and can provide a tool for understanding population-wide impacts of single stage events (e.g., mortality and fecundity). Here, the unique dynamics observed for an isolated population of black drum (Pogonias cromis) and the population-wide impacts of salinity as a driver of young-of-the-year (YOY) survival were investigated. This modeling exercise revealed that the dynamics observed in the black drum population are potentially driven by increased survival in the post-settler/YOY stage and that this increased survival is at least partially a result of the higher salinities that typify the Upper Laguna Madre of Texas, a hypersaline estuary (34% increase in population growth rate across the range of salinity examined). Early maturation in this population was also shown to have the potential to provide infrequent, large pulses of fecundity to the population. Quantifying the population-wide impact of such drivers can place management decisions into the context of the environment and provide both a proof-of-concept for specific management action and realistic expectations for managers and constituents alike. Without such formal quantification, it will be difficult for habitat concepts to move from an abstract management tool to widespread application.

Patterns of reproductive success among reintroduced Atlantic salmon in two Lake Champlain tributaries

Reintroduction programs are increasingly implemented to regenerate self-sustaining salmon populations. The extent to which returning adults successfully produce surviving offspring is useful for informing reintroduction efforts but is often unknown, as is the genetic makeup of those offspring. We investigated the patterns of reproductive success (RS) among returning Atlantic salmon reintroduced as juveniles in two tributaries of Lake Champlain, by combining extensive river surveys and a molecular parentage analysis. Tissue samples collected from returning adults and their young-of-the-year (YOY) offspring produced in the wild were genotyped using microsatellite loci. Our results suggest that a low proportion of returning adults produced the small numbers of YOY detected in either tributary (range 9.9–13.7%, or 17 of 124 and 8 of 81 returning adults, respectively) and that 81.6% and 1.2% of YOY assigned to a pair of sampled returning adults. These results demonstrate that adults (of different life history strategies) can successfully reproduce in both of the studied tributaries (Winooski and Boquet Rivers) and that unsampled individuals could have recolonized a given tributary. Nevertheless, a larger number of breeders would need to produce surviving offspring in subsequent years to demographically augment the reintroduced population whilst avoiding short-term issues associated with low genetic diversity and inbreeding. Our results also point to underlying ecological problems that may have reduced RS and potential genetic issues within the hatchery-reared population being used for supplementation. Further adaptive management will be needed to ensure self-sustaining populations in this system.

Hatching Time and Early Growth of Diplodus sargus sargus Inhabiting a Coastal Area of Gökçeada Island, Turkey

Daily growth increments in sagittal otoliths were used to estimate the age and growth of young of the year (YOY) white seabream, Diplodus sargus sargus collected between June 2013 and June 2014 at 6 different locations in the shallow waters (<20 m) off Gokceada, Turkey. Estimated ages from otolith daily growth increments (DGI) were found 42–238 days old. The mean daily growth rate of YOY D. sargus sargus was estimated as 0.046 cm/day. ANCOVA indicated that there was significant difference in daily growth rates between the locations (F = 22.92, df = 5, P < 0.001). The maximum daily growth rate of 0.055 cm/day was found in the location 2, while the minimum value of 0.037 cm/day was observed in the location 4. Hatching time was determined by subtracting the daily age of the fish from the sampling date and then hatch date frequency distributions were determined to occur from January through June, and 2 main hatching peaks were observed from the different locations. Linear relationships between otolith morphology (otolith length; OL, width; OW and radius; OR) and fish length (TL) were obtained.

Daily growth of young-of-the-year largehead hairtail (Trichiurus japonicus) in relation to environmental variables in the East China Sea

Abstract Largehead hairtail (Trichiurus japonicus) is an important fish species in China Sea, characterized by wide distribution, extensive migration, long spawning period and high economic value. The East China Sea is one of the typical over-exploited ecosystems in the world where most of the fish populations are overfished. In spite of high fishing pressure over an extended period, the catch of largehead hairtail showed an increasing trend in recent years. In this study, using otolith microstructure analysis for daily ageing, we explored spawning seasonality of largehead hairtail and daily growth of young-of-the-year (YoY) largehead hairtail in the East China Sea. Spawning seasonality of largehead hairtail was found to be nearly year round with two dominant seasons: autumn and spring. The gradient forest method was used to identify the relative importance of various environmental variables in relation to daily growth of YoY largehead hairtail; the first six most important environmental variables were subsequently analyzed using generalized additive models for their specific associations with daily growth of YoY largehead hairtail. Results show that sea surface temperature (SST), sea bottom temperature (SBT), temperature difference (TD) between surface and bottom water, and mixed layer depth (MLD) are the most important variables for daily growth of almost all month cohorts. In addition, the consistent interactive effects of water temperature (SST and SBT) and MLD suggest that daily growth of YoY largehead hairtail is influenced by the interactive effects of water temperature and nutrient supplies. This study highlights the importance of understanding the reproductive process and early growth of largehead hairtail in relation to environmental variables, which has important implications for the sustainable management and utilization of largehead hairtail in the over-exploited China Seas.

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment.

While the population growth rate in long‐lived species is highly sensitive to adult survival, reproduction can also significantly drive population dynamics. Reproductive parameters can be challenging to estimate as breeders and nonbreeders may vary in resighting probability and reproductive status may be difficult to assess. We extended capture–recapture (CR) models previously fitted for data on other long‐lived marine mammals to estimate demographic parameters while accounting for detection heterogeneity between individuals and state uncertainty regarding reproductive status. We applied this model to data on 106 adult female bottlenose dolphins observed over 13 years. The detection probability differed depending on breeding status. Concerning state uncertainty, offspring were not always sighted with their mother, and older calves were easier to detect than young‐of‐the‐year (YOY), respectively, 0.79 (95% CI 0.59–0.90) and 0.58 (95% CI 0.46–0.68). This possibly led to inaccurate reproductive status assignment of females. Adult female survival probability was high (0.97 CI 95% 0.96–0.98) and did not differ according to breeding status. Young‐of‐the‐year and 1‐year‐old calves had a significantly higher survival rate than 2‐year‐old (respectively, 0.66 CI 95% 0.50–0.78 and 0.45 CI 95% 0.29–0.61). This reduced survival is probably related to weaning, a period during which young are exposed to more risks since they lose protection and feeding from the mother. The probability of having a new YOY was high for breeding females that had raised a calf to the age of 3 or lost a 2‐year‐old calf (0.71, CI 95% 0.45–0.88). Yet, this probability was much lower for nonbreeding females and breeding females that had lost a YOY or a 1‐year‐old calf (0.33, 95% CI 0.26–0.42). The multievent CR framework we used is highly flexible and could be easily modified for other study questions or taxa (marine or terrestrial) aimed at modeling reproductive parameters.

An analysis of the fish assemblages around 23 oil and gas platforms off California with comparisons with natural habitats

Between 1995 and 2013, we surveyed fishes living around 23 California offshore oil and gas platforms (midwaters, bases, and shell mounds) and 70 natural habitats. These platforms were distributed between about Point Arguello, central California, and Huntington Beach, southern California, had seafloor depths between 49 and 363 m, and were surveyed between one and 16 times. A total of 1,526,437 fishes were observed. Fish densities were highest around platform bases, followed by platform midwaters, shell mounds, and natural habitats. Of all fishes observed, 90.4% were in the genus Sebastes. Water depth was the strongest driver of the fish species assemblages, although habitat type and geographic location were also important. Most of the fishes living around platforms and natural habitats were relatively small, primarily ≤20 cm in length. Many of these individuals were the juveniles of larger taxa or the juveniles and adults of dwarf species. Larger fishes were less common and these were most often found around platform bases and on natural habitats. Most young-of-the-year (YOY) fishes occurred at water depths of ≤150 m at all four habitats. At platforms, YOY densities were highest in platform midwaters and bases. On average, densities of these young fishes were somewhat higher compared to natural habitats and it is likely that many, although not all, California platforms play a significant role as nursery grounds for a variety of fishes, particularly for a number of Sebastes species.