Serial depletion of marine invertebrates leads to the decline of a strongly interacting grazer

University of Washington, Department of Biology, Box 351800, Seattle, Washington 98195-1800, USA.
Ecological Applications (Impact Factor: 4.09). 10/2007; 17(6):1752-70. DOI: 10.1890/06-1369.1
Source: PubMed


We investigated the relative roles of natural factors and shoreline harvest leading to recent declines of the black leather chiton (Katharina tunicata) on the outer Kenai Peninsula, Alaska (U.S.A.). This intertidal mollusk is a strongly interacting grazer and a culturally important subsistence fishery for Sugpiaq (Chugach Alutiiq) natives. We took multiple approaches to determine causes of decline. Field surveys examined the significant predictors of Katharina density and biomass across 11 sites varying in harvest pressure, and an integrated analysis of archaeological faunal remains, historical records, traditional ecological knowledge, and contemporary subsistence invertebrate landings examined changes in subsistence practices through time. Strong evidence suggests that current spatial variation in Katharina density and biomass is driven by both human exploitation and sea otter (Enhydra lutris) predation. Traditional knowledge, calibrated by subsistence harvest data, further revealed that several benthic marine invertebrates (sea urchin, crab, clams, and cockles) have declined serially beginning in the 1960s, with reduced densities and sizes of Katharina being the most recent. The timing of these declines was coincident with changes in human behavior (from semi-nomadic to increasingly permanent settlement patterns, improved extractive technologies, regional commercial crustacean exploitation, the erosion of culturally based season and size restrictions) and with the reestablishment of sea otters. We propose that a spatial concentration in shoreline collection pressure through time, increased harvest efficiency, and the serial depletion of alternative marine invertebrate prey have led to intensified per capita predator impacts on Katharina and thus its recent localized decline.

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    • "success. TEK can be used directly or indirectly to fill the many data gaps that exist in species and habitat distributions and dynamics (e.g., there are almost no fisheries-independent spatial data for fishes) (Salomon et al., 2007). Thus, the proposed MPAs are likely more effective at representing features than our data can show, given the data gaps. "
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    ABSTRACT: We assessed the effectiveness of existing and proposed MPAs.•We estimated the ecological effectiveness of different levels of protection.•We assessed representation, size, spacing, and governance considerations.•Existing MPAs fell short of meeting targets in the study region.•Effectiveness estimates should be applied in MPAs elsewhere.
    Biological Conservation 12/2014; 180. DOI:10.1016/j.biocon.2014.09.037 · 3.76 Impact Factor
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    • "In the absence of predation by otters, as a result of enhanced longevity, invertebrate prey frequently become “hyper-abundant” and attain much larger sizes [18], [19], [20]. Despite these well-known effects on shallow subtidal populations and communities, few studies have investigated how otters influence intertidal communities (but see [21], [22], [23]), and none to our knowledge on the structurally complex mussel beds that are characteristic of temperate rocky intertidal communities throughout the northeast Pacific. "
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    PLoS ONE 05/2013; 8(5):e65435. DOI:10.1371/journal.pone.0065435 · 3.23 Impact Factor
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    ABSTRACT: The long-term impacts of large hydroelectric dams on small-scale fisheries in tropical rivers are poorly known. A promising way to investigate such impacts is to compare and integrate the local ecological knowledge (LEK) of resource users with biological data for the same region. We analyzed the accuracy of fishers' LEK to investigate fisheries dynamics and environmental changes in the Lower Tocantins River (Brazilian Amazon) downstream from a large dam. We estimated fishers' LEK through interviews with 300 fishers in nine villages and collected data on 601 fish landings in five of these villages, 22 years after the dam's establishment (2006-2008). We compared these two databases with each other and with data on fish landings from before the dam's establishment (1981) gathered from the literature. The data obtained based on the fishers' LEK (interviews) and from fisheries agreed regarding the primary fish species caught, the most commonly used type of fishing gear (gill nets) and even the most often used gill net mesh sizes but disagreed regarding seasonal fish abundance. According to the interviewed fishers, the primary environmental changes that occurred after the impoundment were an overall decrease in fish abundance, an increase in the abundance of some fish species and, possibly, the local extinction of a commercial fish species (Semaprochilodus brama). These changes were corroborated by comparing fish landings sampled before and 22 years after the impoundment, which indicated changes in the composition of fish landings and a decrease in the total annual fish production. Our results reinforce the hypothesis that large dams may adversely affect small-scale fisheries downstream and establish a feasible approach for applying fishers' LEK to fisheries management, especially in regions with a low research capacity.
    Ecological Applications 03/2013; 23(2):392-407. DOI:10.2307/23441004 · 4.09 Impact Factor
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