Trawl avoidance as a source of error in estimates of the prevalence of Icthyophonus hoferi disease in Norwegian spring spawning herring (Clupea harengus L.) in the feeding area

Summary: Results are presented from a survey in the Norwegian Sea in the summer 1993, where the abundance and distribution of herring was investigated, using a high resolution sonar and pelagic trawling at the surface. An index of avoidance was constructed by comparing the catch to be expected from the sonar registrations of the number of schools and the amount of scattered registrations, with the actual catch in each haul. This index was negatively correlated to the frequency of diseased herring in the catch. This indicates that diseased herring is less capable of avoiding the trawl. Application of this result for estimating the true disease prevalence is discussed

En verktøykasse for aldersstrukturerte bestandsberegninger basert på fangst- og overvåkingsdata (TASACS)

TASACS (A Toolbox for Age-structured Stock Assessment using Catch and Survey data) is a collection of computer programs for performing routine analytic assessments of fish stocks. It consists of programs for making assessments and a working environment for handling input data, organizing the work and displaying results and diagnostics. The paper gives a detailed description of the methods and an outline of the working environment

Trawl avoidance as a source of error in estimates of the prevalence of Icthyophonus hoferi disease in Norwegian spring spawning herring (Clupea harengus L.) in the feeding area

Summary: Results are presented from a survey in the Norwegian Sea in the summer 1993, where the abundance and distribution of herring was investigated, using a high resolution sonar and pelagic trawling at the surface. An index of avoidance was constructed by comparing the catch to be expected from the sonar registrations of the number of schools and the amount of scattered registrations, with the actual catch in each haul. This index was negatively correlated to the frequency of diseased herring in the catch. This indicates that diseased herring is less capable of avoiding the trawl. Application of this result for estimating the true disease prevalence is discussed

Cambios en la abundancia y distribución espacial del estornino del Atlántico (Scomber colias) en el ecosistema pelágico y pesquerias de Portugal

This study describes changes in abundance and spatial distribution of Atlantic chub mackerel in the Portuguese waters and the Spanish waters of the Gulf of Cadiz using data from acoustic surveys from 1995 to 2010 and data from the fishery since 1958. The distribution and dynamics of chub mackerel and sardine (Sardina pilchardus) are compared and species interactions are discussed. From 2007 to 2009, chub mackerel biomass, as measured acoustically, ranged between 69000 and 238000 t concentrated off the western coast (~50%) and in the Gulf of Cadiz (~30%). Portuguese landings have varied with periods of high landings around 1970 and in recent years. Since 1986 landings have been between 4000 and 23000 t. Both survey catches and commercial landings are taken mainly off the southwestern coast and one- to two-year-old individuals (20-24 cm) predominate in both. Scarcity of larger individuals may be a consequence of their deeper distribution and avoidance of fishing gear, migration of older individuals or a combination of both. In years with high abundance, the fishery expands to the northwestern areas of the Iberian Peninsula. The expansion appears to be caused by improved recruitment although other factors might have contributed (such as targeting to compensate for low sardine catches and the appearance of new markets). The complementary spatial distribution of chub mackerel and sardine and the inverse correlations between their frequency of occurrence, landings and recruitment indices suggest some interaction between the dynamics of the two species, possibly associated with climatic variation.Este estudio describe los cambios en la abundancia y distribución espacial del estornino del Atlántico en las aguas portuguesas y aguas españolas del golfo de Cádiz a partir de datos de las prospecciones acústicas 1995-2010 y datos de la pesquería desde 1958. La distribución y la dinámica del estornino y de la sardina (Sardina pilchardus) se comparan y se analiza la interacción de las especies. Durante 2007-2009, la biomasa del estornino medida acústicamente osciló entre 69 y 238 mil t y se concentró frente a la costa occidental (~50%) y en el golfo de Cádiz (~30%). Los desembarques portugueses han variado con períodos de altas capturas alrededor de 1970 y en los últimos años. Desde 1986 los desembarques han sido entre 4 y 23 mil t. Ambas capturas de campañas y desembarques comerciales se toman principalmente en la costa sur occidental y individuos de 1-2 años edad (20 a 24 cm) predominan en ambos. La escasez de individuos más grandes puede ser una consecuencia de su distribución más profunda y la evitación de las artes de pesca, la migración de los individuos mayores o una combinación de ambos. En los años de mucha abundancia, la pesquería se expande a las áreas occidentales norte de la Península Ibérica. La expansión parece ser causada por un mejor reclutamiento aunque otros factores pueden haber contribuido (pesca dirigida para compensar las capturas bajas de sardina y la aparición de nuevos mercados). La distribución espacial complementaria de caballa y de sardina y la correlación inversa entre la frecuencia de ocurrencia, los desembarques y los índices de reclutamiento sugieren una interacción entre la dinámica de las dos especies, posiblemente asociados a las variaciones climáticas

Environmental information for stock evaluation and management advice purposes

This report summarizes the work of an internal working group appointed by the Institute of Marine Research's management group to evaluate inclusion of environmental parameters in stock evaluation. The report discusses the current and potential usage of environmental information and presents specific recommendation on how to increase the usage of environmental information for stock evaluation and management advice purposes. NORSK SAMMENDRAG: Rapporten sammenfatter arbeidet til et utvalg nedsatt av ledergruppen ved Havforskningsinstituttet for å evaluere bruk av miljøinformasjon i bestandsvurdering og rådgivning. Rapporten diskuterer dagens- og potensiell bruk av miljøinformasjon og gir konkrete anbefalinger for hvordan Havforskningsinstituttet kan øke bruken av miljøinformasjon i bestandsvurderinger og rådgivning

Reference points for the Iberian sardine stock (ICES areas VIIIc and IXa)

Three Yield-Per-Recruit/stock-recruitment approaches (deterministic, stochastic with plotMSY and stochastic with HCS) were used to explore reference points for the management of the Iberian sardine. The sensitivity of reference points was evaluated in relation to alternative scenarios of productivity, growth and selectivity. Growth and selectivity scenarios had a small impact on stock projections whereas productivity scenarios were very influential. The three approaches gave coherent results, but the approach using HCS, assuming uncertainty in stock biology and recruitment dynamics, was preferred to derive reference points for sardine. In this approach, the risks of the stock fa lling below some low biomass level can also be taken into account. This possibility was considered to be useful in the case of the sardine for which exploitation at maximum YPR or F0.1 resulted in values above historical exploitation and higher than Floss, therefore unsuitable as precautionary management targets. Bloss (306 thousand t) is proposed as a proxy for Blim but given no indication that recruitment is impaired below this biomass level, the group considers that the level of risk of falling below this candidate for Blim acceptable in the evaluation of a management plan should be higher than the standard ICES value (5%).The stock productivity has declined over time; therefore a scenario of low productivity was assumed (recruitment in the period 1993-2010). Under this productivity scenario, the Fmsy value for the sardine stock is 0.34, a value associated with a high probability (45%) of the biomass falling below the proposed Blim and therefore, incompatible with precautionary considerations. The WG proposes an F= 0.27, corresponding to a Prob(B<Blim)<15% under equilibrium, as the best available candidate for an F management target (proxy for Fmsy) assuming the low productivity scenario (since 1993) will continue in the future. This F provides high yield conditional to a low probability that the biomass falls below Blim=Bloss in equilibrium, thus incorporating precautionary considerations

Growth patterns in the North Sea and western mackerel in Norwegian catches 1960- 85

Length, weight and age in random samples from Norwegian catches of' mackerel from 1960 to 1985 have been reviewed. A standard growth curve was constructed by applying a modified von Bertalanffy equation to all data. The deviation from this curve is largely independent of age for adult mackerel, and may be used as a measure of the growth pattern. In the North Sea area, the length at age has increased gradually by 4-5 cm during this period, while it has been nearly stationary in the western spawning area. The condition has remained stable in this period. The mackerel caught in the North Sea is generally larger at age than the typical Western mackerel, even in the years and seasons when Western mackerel dominated in the cathes in the North Sea. The mixing of two stock components with different growth patterns also makes the use of length distributions as a measure of age distributions questionable

Stock prediction using stochastic recruitment numbers with empirical stock-dependent distribution

Probability distributions for the recruitment, conditional on the spawning stock biomass (SSB) were made using a kernel method. Predictions were made with recruitments according to these distributions for 10 years, using a Monte Carlo procedure, assuming constant weight at age, maturity ogive and natural mortality. Examples are given for 3 stocks, Western mackerel, North Sea sandeel and North Sea herring. Three management strategies were studied, a fixed F, a fixed yearly catch and a regime aiming at stabilizing the SSB. Due to the variable recruitment, attempts to stabilize the SSB increases the year to year variations in the yield. Attempting to take a fixed catch every year is hazardous, since the appearance of a few poor year classes may detoriate the stock so that the future recruitment suffers. This simple approach may be a useful tool for evaluating management strategies in terms of risks and possible outcome of the fisheries

Ichthyophonus hoferi disease in the herring in Norwegian waters

After the discovery of I. hoferi disease in Norwegian spring spawning herring in summer 1991, a program for systematic surveillance of the disease in the herring in Norwegian waters was developed. The programme, which aims primarily at monitoring the prevalence of the disease, is described. Macroscopic lesions in the heart emerged as the standard diagnostic criterium. The results so far indicate that the situation for Norwegian spring spawning herring is not alarming, altohough it still deserves attention. For the North Sea herring, the situation is less clear. The diseased herring seem to be less prone to follow normal scooling behavior, which causes sampling problems that must be taken into account when interpreting prevalence results

Migration of western mackerel to the North Sea 1973 - 1988

The latest years, it is evident that most of the mackerel present in the North Sea belongs to the Western stock, since the yearly catches by far exceed the presumed size of the North Sea stock. The Norwegian tagging data have been revised to obtain estimates of the percentage of Western mackerel in the catches in the North Sea. By combining these data with the distribution of catches, a reasonable estimate of the migration of the Western mackerel to the North Sea may be obtained