Efficiency of Sonar Fish Protection Device at the Kokaral Dam of the Small Aral Sea

The study aimed to assess the efficiency of the pilot hydro-acoustic (sonar) fish protection device (SFPD) installed at the Kokaral Dam of the Small Aral Sea. For this purpose, between August 27 and September 5, 2020 experimental and control fish catching was carried out using fixed fishing nets (30×60 mm mesh). The SFPD’s effectiveness was assessed based on the amount and species diversity of the caught fish with and without the SFPD operating. Fish behavior and distribution were monitored using an echo sounder. In terms of quantity, 173 fish were caught with the SFPD off, and 94 with the SFPD on. In terms of biomass, the values were 37.5 kg and 27.6 kg, respectively. With the SFPD off, the ichthyofauna composition was represented by 12 fish species: carp, crucian carp, roach, ide, bream, common rudd, saber carp, snakehead, pike perch, perch, pike, and asp. With the SFPD on, roach and ide were absent in the catch, and the quantity of common rudd significantly decreased. In both catches, the quantity of carp and crucian carp was similar; bream and saber carp specimen were sporadic. The number of predatory fish (pike, perch, snakeheads, and pike perch) in the catches increased. Asp was absent in the net catches also; however, this fish species represents the main object of amateur hook and line fishing. Based on the catch-per-effort unit, it can be concluded that whereas the SFPD observed efficiency for small non-predatory fish like ide, roach, and common rudd was 95%, it was 0% for large non-predatory fish (carp and crucian carp); and negative for predatory fish.

Modelling of stock dynamics for spiny king crab Paralithodes brevipes at southern Kuril Islands using a finite-difference model with delay

The information on fishery object limited by CPUE data and fragmentary data on age and size is sufficient for production models. However, this type of models is improper for long-living species, as crabs, because of problem with assumption on equilibrium stock. Describing dynamics of a single year-class, these models average the parameters for all generations that impedes to use them for assessment of crabs stocks. Finite-difference models with delay are more promising in this case. Deriso-Snute finite-difference model with delay was used for simulating of the spiny king crab biomass dynamics at southern Kuril Islands and forecasting of TAC for this species. Parameters of the model were estimated using the algorithm of sampling by scheme of Markov chain. The model is relatively simple and undemanding to data - time-series of commercial catch per effort is sufficient for its simplest version. Results of modeling are comparable with the results of cohort models.

Subjective judgement in data subsetting: implications for CPUE standardisation and stock assessment of non-target chondrichthyans

Standardisation of catch-per-effort (CPUE) data is an essential component for nearly all stock assessments. The first step in CPUE standardisation is to separate the comparable from the non-comparable catch and effort records and this is normally done based on subjective rules. In the present study, we used catch-and-effort data from the elephant fish (Callorhinchus milii) to illustrate the differences in CPUE when using expert judgement to define different ad hoc selection criteria used to subset these data. The data subsets were then used in the standardisation of CPUE and the stock assessment of elephant fish. The catch-and-effort subsets produced different patterns of precision and trends, each of which led to different estimates (and related uncertainty) of model parameters and management reference points. For most CPUE series, there was a very high probability that the elephant fish stock is overexploited and that overfishing is occurring. The estimates of total allowable catch (TAC) and the uncertainty around these estimates also varied considerably depending on the CPUE series used. Our study shows how sensitive TAC estimation is when there is high uncertainty in the definition of the fishing effort targeted at the species analysed.

Trends in trawl and purse seine catch rates in the north-eastern Mediterranean

Data on fishing effort expressed in vessel days at sea and corresponding landing/day for a large number of species have been collected by the Institute of Marine Biological Resources (IMBR) since the second half of 1995. Data were collected over a grid of 21 stations throughout the Greek seas. In the present study we analyzed the monthly days at sea as well as catch per day for trawlers and purse seiners from 1996 to 2000, by general linear models and trend analysis. The following vessel size groups per gear were considered: (a) trawlers smaller and larger than 20m; (b) purse-seiners smaller and larger than 15m. Collected data were also aggregated for five fishing sub-areas: the North Aegean, the Central Aegean, the South Aegean, Cretan waters and the Ionian Sea. Trend analysis of landing/day time series indicated that demersal and pelagic resources are declining in the main fishing grounds. Declining landing/day trends are regarded as indicators of overfishing, especially in the light of the fact that high catch rates are maintained by fishing in ‘hot spots’. The results of the present analysis provide, for the first time, important information on the sustainability of the fisheries in the north-eastern Mediterranean, an area characterized by a complete lack of accurate long-term data on effort and catch per effort

Balancing Fisheries Management and Water Uses for Impounded River Systems

<em>Abstract</em>.—The propensity of adult crappies <em>Pomoxis </em>spp. to use similar locations during and among spawning seasons in reservoirs is unknown. This study proposed to determine adult crappie abundance, fidelity, and the substrate consistency in five coves at Sherman Reservoir, Nebraska, which historically displays a quality crappie fishery. Adult crappies (≥150 mm total length) were collected with trap nets from each cove during May 2004 to 2006 and tagged with a visible implant elastomer tag that was color coded for each cove. A total of 7,041 crappies were tagged in 2004, 5,868 in 2005, and 3,967 in 2006. The mean catch per effort in coves ranged from 40 to 75 fish/net-night in this study. Cove fidelity, defined as percent of tagged crappie recaptured in the same cove, within a year ranged from 74% to 88% in 2004, 84–88% in 2005, and 65–89% in 2006. Cove fidelity between spawning seasons was 62–81% for 2004 and 2005, 56–90% for 2005 and 2006, and 47–92% for 2004 and 2006. All five coves had a loam substrate with similar firmness. These data indicate a tendency by crappie to visit the same cove during successive spawning seasons, even when comparable substrates are available, which demonstrates the need for habitat conservation efforts for specific coves used during spawning seasons.

Folly and fantasy in the analysis of spatial catch rate data

Spatial catch per effort data can provide useful indices of population trends provided that they are averaged so as to correct for effects of changes in the distribution of fishing activity. Simple, nonspatial ratio estimates should not be used in such analyses. The averaging for any time period must necessarily make some assumptions about what catch rates would have been in spatial strata that had not yet, or were no longer, being fished. Ignoring the unfished strata (averaging only over the areas that were fished) amounts to assuming that they behaved the same as the fished strata and can lead to severe hyperdepletion in abundance indices for fisheries that developed progressively over large regions.