Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf

We tested the hypothesis that recent oceanographic changes associated with climate change in the Northeast United States continental shelf ecosystem have caused a change in spatial distribution of marine fish. To do this, we analyzed temporal trends from 1968 to 2007 in the mean center of biomass, mean depth, mean temperature of occurrence, and area occupied in each of 36 fish stocks. Temporal trends in distribution were compared to time series of both local-and large-scale environmental variables, as well as estimates of survey abundance. Many stocks spanning several taxonomic groups, life-history strategies, and rates of fishing exhibited a poleward shift in their center of biomass, most with a simultaneous increase in depth, and a few with a concomitant expansion of their northern range. However, distributional changes were highly dependent on the biogeography of each species. Stocks located in the southern extent of the survey area exhibited much greater poleward shifts in center of biomass and some occupied habitats at increasingly greater depths. In contrast, minimal changes in the center of biomass were observed in stocks with distributions limited to the Gulf of Maine, but mean depth of these stocks increased while stock size decreased. Largescale temperature increase and changes in circulation, represented by the Atlantic Multidecadal Oscillation, was the most important factor associated with shifts in the mean center of biomass. Stock size was more often correlated with the total area occupied by each species. These changes in spatial distribution of fish stocks are likely to persist such that stock structure should be re-evaluated for some species

Power of monitoring programmes to detect decline and recovery of rare and vulnerable fish

1. Abundance trends provide key guidance when setting conservation priorities, whether indicating population decline, stability or recovery. Knowledge of the power of surveys to detect trends is essential, as the consequences of not detecting a real trend can be profound. 2. Unfortunately, some surveys have been established with no assessment of power, and others are used to study species that were not their original focus. The latter is common in the marine environment, where rare fish are monitored using catch data from surveys that target more abundant commercially fished species. 3. We calculated the power of a large-scale annual monitoring survey (the English North Sea bottom trawl survey) to detect decline and recovery of species that are vulnerable to fishing. As fisheries exploitation invariably precedes scientific investigation, the survey began after many vulnerable species had already been depleted. 4. The power of the survey to detect declines in the abundance of vulnerable species on time scales of < 10 years was low and the survey often failed to detect declines that would lead to listings under the IUCN A1 Red List criteria. Thus conservation prioritization based solely on survey data may fail to identify species at risk of regional extinction. 5. If conservation measures were effective, and vulnerable populations recovered at the maximum potential rate, 5-10 years of monitoring would often be required to detect recovery. 6. Power to detect trends in abundance was increased by developing a composite indicator that reflected trends in abundance of several vulnerable species. This indicator provided an overview of their conservation status. 7. Synthesis and applications. Consistent with the precautionary principle, conservation prioritization and management action should not depend on the statistical significance of recent abundance trends when low power is a consequence of historical depletion. If the conservation prioritization and management of rare and/or vulnerable species have to be predicated on evidence of significant declines, then higher type 1 error rates (falsely detecting a decline) should be acceptable. This is because the costs of type 1 errors are lower than those of type 2 (failure to detect a real decline)

Improving the definition of fishing effort for important European fleets by accounting for the skipper effect

The scope of this paper is to quantify, for a wide selection of European fisheries, fishing tactics and strategies and to evaluate the benefits of adjusting the definition of. fishing effort using these elements. Fishing tactics and strategies were identified by metiers choices and a series of indices. These indices have been derived to reflect shifts in tactics (within a fishing trip) and in strategies (within a year). The Shannon-Wiener spatial diversity indices of fishing tactics (FT_SW) and strategies (YE_SW) had the greatest impact on catch rates. In particular, FT_SW was always negatively correlated to catch rates. One may anticipate that during a fishing trip, vessels with high FT_SW have been searching fish aggregations for a long time, while vessels with low FT_SW have been more efficient in finding these aggregations. The linkage between YE_SW and catch rates was of a more complex nature. Adjusting fishing effort by means of (i) the metier effect and (ii) the indices of tactics and strategies generally led to a substantial gain in the precision of the relationship between fishing mortality and fishing effort

Measuring marine fish biodiversity: temporal changes in abundance, life history and demography

Patterns in marine fish biodiversity can be assessed by quantifying temporal variation in rate of population change, abundance, life history and demography concomitant with long-term reductions in abundance. Based on data for 177 populations (62 species) from four north-temperate oceanic regions (Northeast Atlantic and Pacific, Northwest Atlantic, North mid-Atlantic), 81% of the populations in decline prior to 1992 experienced reductions in their rate of loss thereafter; species whose rate of population decline accelerated after 1992 were predominantly top predators such as Atlantic cod (Gadus morhua), sole (Solea solea) and pelagic sharks. Combining population data across regions and species, marine fish have declined 35% since 1978 and are currently less than 70% of recorded maxima; demersal species are generally at historic lows, pelagic species are generally stable or increasing in abundance. Declines by demersal species have been associated with substantive increases in pelagic species, a pattern consistent with the hypothesis that increases in the latter may be attributable to reduced predation mortality. There is a need to determine the consequences to population growth effected by the reductions in age (21%) and size (13%) at maturity and in mean age (5%) and size (18%) of spawners, concomitant with population decline. We conclude that reductions in the rate of population decline, in the absence of targets for population increase, will be insufficient to effect a recovery of marine fish biodiversity, and that great care must be exercised when interpreting multi-species patterns in abundance. Of fundamental importance is the need to explain the geographical, species-specific and habitat biases that pervade patterns of marine fish recovery and biodiversity