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Abstract: Since 1996, the Peruvian Marine Research Institute (IMARPE) has been collecting data on catches by vessel, species, weight (kg), gear type and fishing grounds for all major ports of the artisanal fishery. At present, this fishery has exclusive rights to undertake commercial fishing operations within 5 miles from the Peruvian coast. During this period there have been significant changes in the composition and spatial pattern of the artisanal fishery including a reduction in catch of sardine and mullet, and increases in catches of jumbo squid, scallops and dolphin fish. Of particular note was the effect of the El Niño of 1997–1998, with a major reduction in the catch of anchovy and silversides and increases in shellfish (mussels and scallops), reflecting a shift during this period from a pelagic to a benthic dominated system. While the fishery has undergone relatively large changes in species composition of catches there has been a relatively steady level of catch per trip for target species and a modest decrease in numbers of trips in the fishery. To some extent the observed changes reflect changes in environmental conditions, with a warmer period before 1999 and a cooler, higher upwelling period since then. The environmental changes were accompanied by the rapid increase of jumbo squid, a voracious predator on many commercial fish species since 1999. However, some changes reflect changes in economic conditions, for example higher oil prices and decreased selling price of many species resulting an increased focus on high value fisheries and exports including the use of set lines to produce a higher quality end-product and the holding of shellfish in pens in the sea to increase their size and bring a higher price. The Peruvian artisanal fishery features strong seasonal variation in some species, generally sustained catches over a long time period, but changes in species dominance in the catches, reflecting a long-term regime-shift-like pattern in this highly productive region as well as the generalist nature of the fishery. [Copyright &y& Elsevier]

Abstract: The Humboldt Current System, like all upwelling systems, has dramatic quantities of plankton-feeding fish, which suggested that their population dynamics may ‘drive’ or ‘control’ ecosystem dynamics. With this in mind we analysed the relationship between forage fish populations and their main prey, zooplankton populations. Our study combined a zooplankton sampling program (1961–2005) with simultaneous acoustic observations on fish from 40 pelagic surveys (1983–2005) conducted by the Peruvian Marine Research Institute (IMARPE) and landing statistics for anchoveta (Engraulis ringens) and sardine (Sardinops sagax) along the Peruvian coast from 1961 to 2005. The multi-year trend of anchoveta population abundance varied consistently with zooplankton biovolume trend, suggesting bottom-up control on anchovy at the population scale (since oceanographic conditions and phytoplankton production support the changes in zooplankton abundance). For a finer-scale analysis (km) we statistically modelled zooplankton biovolume as a function of geographical (latitude and distance from the 200-m isobath), environmental (sea surface temperature), temporal (year, month and time-of-day) and biological (acoustic anchovy and sardine biomass within 5km of each zooplankton sample) covariates over all survey using both classification and regression trees (CART) and generalized additive models (GAM). CART showed local anchoveta density to have the strongest effect on zooplankton biovolume, with significantly reduced levels of biovolume for higher neighbourhood anchoveta biomass. Additionally, zooplankton biovolume was higher offshore than on the shelf. GAM results corroborated the CART findings, also showing a clear diel effect on zooplankton biovolume, probably due to diel migration or daytime net avoidance. Apparently, the observed multi-year population scale bottom-up control is not inconsistent with local depletion of zooplankton when anchoveta are locally abundant, since the latter effect was observed over a wide range of overall anchoveta abundance. [Copyright &y& Elsevier]

Abstract: The Humboldt Current System (HCS) is dominated by two pelagic species; Peruvian anchovy or anchoveta (Engraulis ringens) and sardine (Sardinops sagax). Using data from 43 acoustic surveys conducted from 1983 through 2005 by the Peruvian Marine Institute (IMARPE), we examined the distribution of these two species relative to water masses. We tested the hypothesis that anchovy was found more frequently in upwelled cold coastal water (CCW) and mixed waters (MCW) than in other water types and that sardine was more associated with more offshore oceanic surface subtropical water (SSW). Surface temperature, salinity, latitude, season and distance to the coast data were used to define water masses. Results using generalized additive models (GAM), modelling sardine and anchovy presence–absence as a function of year, water body, bottom depth and latitude, showed that anchovy were primarily found in CCW and MCS, while sardine were more ubiquitous relative to water masses with some predilection for SSW. These results were supported by various indexes of anchovy and sardine distribution versus water mass as well as temporal and location variables. [Copyright &y& Elsevier]

Abstract: The Pribilof Islands region is recognized to be a major nursery for age-0 walleye pollock (Theragra chalcogramma) in the eastern Bering Sea. However, the Pribilof Islands’ importance for the recruitment of pollock in the Bering Sea has not been quantified. In this paper, we define the geographic extent of the Pribilof Islands region based on ocean circulation, location of major fronts, and trophic interactions. The abundance and distribution by oceanographic habitat (nearshore, frontal and offshore), of acoustically determined age-0 pollock are compared between the Pribilof Islands and the Inner Front of the eastern Bering Sea, for the summers of 1997–1999. Net samples collected during surveys in 1995–2002 are used to compare the abundance of age-0 pollock in the Pribilof Islands region to locations eastward along the Bering Sea shelf. We found densities of age-0 pollock near the Pribilof Islands to be generally higher than on the surrounding shelf, and higher or non-significantly different from the Inner Front. Through synthesis of our data and inferences of pollock growth and mortality, we estimate the Pribilof Islands region to have comprised 12.5% (1997), 53.7% (1998), and 24.7% (1999) of the total stock of age-0 pollock in the eastern Bering Sea. Since the Pribilof Islands region comprises only 14% of the total eastern Bering Sea area, evidence is given that a disproportionally large fraction of the age-0 pollock population inhabits the Pribilof Islands nursery. [Copyright &y& Elsevier]

Abstract: This paper examines the relationship between poleward and equatorward current patterns and the spatial distribution of euphausiids based on acoustic survey data collected in summer 1995 and 1998 in the California Current Ecosystem. Contiguous poleward (usually an undercurrent) and equatorward near-surface current core areas were identified by applying current velocity and distance thresholds along each survey transect. Both currents were pervasive along the coast, but poleward volume transport in both years was about an order of magnitude greater than the equatorward near-surface current volume transports. The poleward volume transport was higher in 1998 than in 1995, especially north of Cape Blanco. The poleward transport centroid was generally further offshore than the surface transport centroid, and was closer to the slope in 1998 than in 1995. The depth centroid of euphausiid patches was generally shallower than the depth centroid of the poleward volume transport centroids. The onshore–offshore location of euphausiid patches was significantly related to the location of the poleward transport centroids, although not in all regions. The patches were not related to the location of equatorward near-surface transport centroids. Differences in the north–south euphausiid distribution were observed between 1995 and 1998. In 1995, there was a much higher abundance of euphausiids in the region immediately north of Cape Blanco, while in 1998, euphausiid abundance was high throughout the survey area. We hypothesize this difference to be in part a result of differences in current patterns between the 2 years and the manner in which currents interact with euphausiid diel migration. [Copyright &y& Elsevier]

The waters around the Pribilof Islands, in the southeast Bering Sea, are a main nursery area for age-0 pollock. Each summer, the islands are surrounded by a well-mixed inshore region, separated from a stratified offshore region by a frontal zone. To study the spatial distribution of age-0 pollock around this frontal structure in relation to physical and biological factors that are likely to influence it, such as advection, age-0 pollock feeding, and predation, samples were collected during September of four consecutive years, 1994–97, along two transects. Samples collected included water column hydrography and currents, acoustic backscatter, and groundfish predator density.Our analysis suggested that different mechanisms may be involved in controlling age-0 pollock distribution north and south of the islands. On the shelf area north of the islands, high age-0 pollock density was significantly associated with areas of high potential for growth only in years or portions of the frontal transect in which predator numbers were relatively low, indicating the importance of predation in controlling fish distribution in this area. In contrast, south of the islands, age-0 pollock distribution was associated more with prey availability, which appeared to be determined by vertical spatial overlap between predators and prey. Moreover, south of the islands, the stronger geostrophic currents, typical of the slope region, were more likely to affect the overall standing biomass of juvenile pollock, by constantly advecting fish away from the area. [Copyright &y& Elsevier]