On the intraspecific competition of yellowfin sole Limanda aspera (Pallas, [1814]) (Pleuronectidae) in the eastern part of the Sea of Okhotsk

Based on the longterm observations for 1963–2019, the article provides an assessment of the yellowfin sole generation mortality dynamics depending initial abundance and population dynamics in view of abundance and biomass. Individual growth and matiration rates were evaluated in generations with different initial abundance and in different states of population dynamics. Results indicated about intraspecific competition in yellowfin sole in the eastern part of the Sea of Okhotsk, expressed in specifics of the dynamics of stock abundance, growth and maturation. Forming generation stock abundance in early and later ages has different character. The more exceeding number of parental eggs spawned, the more generation abundance of yearlings getting exactly compensated by mortality (complete compensation). Older generations demonstrate the phenomen of “overcompensation”, when mortality of generations appeared in the years of higher egg production exceeds fertility. In the period of population growth and stabilization at a high level the period of the Yellowfin sole abundance fluctuation cycle gets shorter and the amplitude – smaller. Effects of intraspecific competition on the growth of individuals are revealed. Negative effects of the competition authentically revealed in elder age groups were not observed in younger age groups. An increase of the Yellowfin sole abundance brings negative effects on maturation rate of males with almost no such effects on females. To the greatest extent such effects can be seen in young age groups, at the beginning and middle stage of maturation.

Reconciling conflicting survey indices of abundance prior to stock assessment

Indices of relative abundance are one of the most important inputs into a stock assessment model. For many species, we must rely on several indices that routinely conflict with each other and which may result in biased and uncertain outputs. Here, we explored whether reconciled trends obtained from dynamic factor analysis (DFA) applied to conflicting indices can be used as a trend of relative abundance input into a stock assessment model. We simulated an age-structured population of two coastal shark species in the southeast United States to generate multiple disagreeing indices, reconciled the indices using DFA, and then inserted both the multiple conflicting survey indices and the simplified DFA-predicted trend into respective stock assessment models. We compared the results of each stock assessment model to simulated values to evaluate the relative performance of each approach. We found that the DFA-based assessment generally performed similarly to the conflicting index-based assessment and may be a useful assessment tool in situations where conflicting indices with different selectivities, catchabilities, variances, and missing data are present. DFA assessment results were more consistent across simulation scenarios and outperformed many conflicting index assessments when surveys underwent shifts in catchability and the underlying stock abundance exhibited contrast.

Some peculiarities of saffron cod Eleginus gracilis (Tilesius) biology and distribution on South-East Kamchatka

Analysis of Danish seine catches from the coastal waters of South-East Kamchatka has revealed all seasonal distribution of saffron cod connected to the sites of the continental sandbanks influenced by aquatic vortexes with increased benthic biomass, where the catches could reach 2.5 t/fishing operation. Based on the data of the trawl and Danish seine surveying, the stock abundance, the occurence frequency, the catches of saffron cod and the contribution into the total catch in the area mentioned increased in the fall-winter period, but could not be characterized as significant. In the period of the research (2003–2018) the Danish seine catches of saffron cod varied as 1–189 t, averaged 31.8 t. The fish in the Danish seine catches had the body length from 11 to 56 cm and the body weight from 20 to 750 г. The mean length and weight of saffron cod in summer was 30.8 cm and 241.7 g and in winter – 31.2 cm and 301.6 g respectively. Occurrence of independent reproductive groups of saffron cod in the coastal bays and on the shelf of South-East Kamchatka can be suggested based on the data of stock abundance distribution, differences in the size composition and the time of maturity.

Variable predator–prey relations in zooplankton overwintering in Subarctic fjords

Zooplankton predator–prey relations in northern Norwegian fjords are highly variable in time and space, and the mechanisms driving this variability are still poorly understood. Replicate Juday net sampling in October and February from 1983 to 2005, which included five repeated tows from bottom to surface, was conducted in Saltfjord and Mistfjord, northern Norway. The time-series provided evidence of in situ variability in species abundance, as well as seasonal and interannual changes in standing stock abundance. The shallow sill of one fjord caused accumulation of coastal water in the fjord’s basin, while the other fjord’s deeper sill selected denser water of Atlantic origin from the same open shelf habitat. The selective advection caused differences in the immigration of species recruiting to the fjords’ specific overwintering communities of zooplankton. Statistical analyses of the cumulated replicate data indicated significant in situ variability in the spatial density of species. Cases with an abundance of carnivores relating positively to other species probably resulted from the carnivores’ attraction to patches with concentrations of prey. Interspecific negative density relations likely indicated either predator avoidance or substantial trophic activity during the sampling. During years of high abundance, some wintering stocks of carnivores evidently reduced the local stocks of overwintering prey. We conclude that predator–prey interactions and stock variability in Subarctic fjords result from complex bio-geophysical interactions that occur on the scales of local habitats and basin-scale population systems.

Predicting catch per unit effort from a multispecies commercial fishery in Port Phillip Bay, Australia

Quantitative models that predict stock abundance can inform stock assessments and adaptive management that allows for less stringent controls when abundance is high and environmental conditions are suitable, or tightening controls when abundance is low and environmental conditions are least suitable. Absolute estimates of stock abundance are difficult and expensive to obtain, but data from routine reporting in commercial fisheries logbooks can provide an indicator of stock status. Autoregressive integrated moving average (ARIMA) models were constructed using catch per unit effort (CPUE) from commercial fishing in Port Phillip Bay from 1978–79 to 2009–10. Univariate and multivariate models were compared for short-lived species (Sepioteuthis australis), and species represented by 1–2 year-classes (Sillaginodes punctatus) and 5–6 year-classes (Chrysophrys auratus). Simple transfer models incorporating environmental variables produced the best predictive models for all species. Multivariate ARIMA models are dependent on the availability of an appropriate time series of explanatory variables. This study demonstrates an application of time series methods to predict monthly CPUE that is relevant to fisheries for species that are short lived or vulnerable to fishing during short phases in their life history or where high intra-annual variation in stock abundance occurs through environmental variability.

Effects of environmental variability on abundance of commercial marine species in the northern Gulf of California

Studies have shown that environmental variables significantly affect variation in stock abundance of marine populations. The northern Gulf of California (NGC) is a highly productive region of interest due to its fish resources and diversity. Conservation of the marine species inhabiting the region is of public interest. Our study analysed the influence of physical environmental factors on several commercial marine species, using catch per unit effort (CPUE) as a proxy for abundance. Generalized additive models were used to test the significance of selected environmental variables on stock abundance. Deseasonalized cross-correlation analysis was used to examine time-lagged correlations between CPUE and abiotic variables to identify response timings. The results suggest that for most commercial species the sea surface temperature and the long-term climate Pacific Decadal Oscillation index are the predominant predictors for species abundance, followed by the Colorado River discharge. The Multivariate ENSO Index and the Pacific-North American pattern indices also showed specific effects on certain species. The NGC is a highly dynamic region, where species respond to environmental changes according to the characteristics of their life histories.

Evaluating effort regulation in mixed fisheries: a Monte Carlo approach

This paper evaluates whether effort regulation could achieve the goal of protecting low-abundance species in mixed fisheries. We construct a two-species bio-economic model and compare the stock abundance ratio in the end of the fishing season with the ratio prior to the fishing. Fishers’ profit maximization problem is governed by three key factors: (i) the overall efficiency of catching different species (catchability), (ii) the price of different species, and (iii) their ability to catch the favoured species separately from the less-favoured species (separability). Using a Monte Carlo sampling of feasible parameters space, we show that effort regulation has good chances (87% of the cases) of maintaining the end stock ratio near equal levels (1/2< stock ratio <2) when the initial stock ratio is equal. If the initial stock ratio is not equal, however, there is a high risk (about 50% of the cases) that effort control increases differences in the relative species abundances, rather than diminishing them. The effects depend on whether the key factors determining fishing profitability are counteracting or reinforcing each other, and their relative strength. Our results warn against placing too much faith on the ability of effort regulation to protect species at low abundances from excessive exploitation.