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Publications 2015

Authors in bold are/were staff or students of the Institute for Ocean Conservation Science and its founding organization, the Pew Institute for Ocean Science.


Rountos, K.J., Frisk, M.G., Pikitch, E.K. 2015. Are We Catching What They Eat? Moving Beyond Trends in the Mean Trophic Level of Catch. Fisheries 40(8).

Abstract

The mean trophic level of fisheries catch is commonly used to describe and assess temporal trends in fisheries. Though its value as an indicator to evaluate the relative health of fisheries in marine ecosystems has been hotly debated, the metric calculated is clear. We applied this indicator along with a relatively new indicator, the mean trophic level of predator consumption, to 40 Ecopath models around the world. Together, these measures were used to detect where fisheries and marine predators may be targeting similar trophic levels of prey. Globally, the mean trophic levels caught by all fisheries and finfish fisheries were similar to those consumed by marine mammals but significantly higher than those consumed by seabirds and large predatory fish. We found no significant differences between the median trophic levels targeted by forage fisheries and predators. These indicators can inform ecosystembased management, especially when information on predators and fishery interactions are limited or unavailable.

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Pikitch, E.K. 2015. Stop-loss order for forage fish fisheries. Proceedings of the National Academy of Sciences 112(21).

Abstract

Recent literature has highlighted the exceptional importance of forage fish, which include some of the largest fisheries in the world and produce a sizeable share of the global wild marine fish catch (1). Forage species play an essential and valuable supporting role within marine ecosystems by serving as prey for larger species (2, 3). These findings underscore the importance of (i) furthering understanding of the determinants of forage fish collapses, and (ii) of devising exploitation strategies that will maintain their crucial ecological and economic roles. Essington et al. (4) significantly advance understanding on both counts, applying novel methods to uncover fishing's fingerprint in regulating population fluctuations and demonstrating the effectiveness of a simple remedy to prevent collapses.

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Gownaris, N.J., Pikitch, E.K., Ojwang, W.O., Michener, R., Kaufman, L. 2015. Predicting Species' Vulnerability in a Massively Perturbed System: The Fishes of Lake Turkana, Kenya. PLoS ONE 10(5).

Abstract

Background and Trophic Diversity Study
Lake Turkana is an understudied desert lake shared by Kenya and Ethiopia. This system is at the precipice of large-scale changes in ecological function due to climate change and economic development along its major inflowing river, the Omo River. To anticipate response by the fish community to these changes, we quantified trophic diversity for seven ecological disparate species (Alestes baremose, Hydrocynus forskalli, Labeo horie, Lates niloticus, Oreochromis niloticus, Synodontis schall, and Tilapia zillii) using stable isotopes. Based on their marked morphological differentiation, we postulated that dietary niches of these species would be similar in size but show little overlap. The degree of trophic diversity varied greatly among the species studied, refuting our hypothesis regarding dietary niche size. Oreochromis niloticus and L. niloticus had the highest trophic diversity and significantly larger dietary niches than T. zillii, A. baremose and H. forskalli. Low overlap among the dietary niches of the seven species, with the exception of the synodontid catfish S. schall, is consistent with our second hypothesis.

Predicting Species' Vulnerability
Breeding vulnerability was highest among those species with the lowest trophic diversity. We predict that in suffering two strikes against them, A. baremose, H. forskalli, T. zillii, and L. horie will be most affected by the highly altered Lake Turkana ecosystem and that O. niloticus, L. niloticus and S. schall will be least affected. Low vulnerability among O. niloticus and L. niloticus is promising for the future of the lake's fishery, but the third most important fishery species (L. horie) will be highly vulnerable to impending ecosystem change. T. zillii should be treated as separate from O. niloticus in the fishery given higher sensitivity and a different ecological role. We see potential for expansion of the fishery for S. schall but don't recommend the development of a fishery for A. baremose and H. forskalli.

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Gownaris, N. 2015. Understanding the Impacts of Changes in Water Inflow on the Fishes of Lake Turkana, Kenya. Dissertation.

Abstract

Lake Turkana, Kenya is an understudied desert lake that receives over 90% of its inflow from the Omo River in Ethiopia. The volume and patterns of inflow from this river influence the lake's chemistry and productivity, as well as the availability of habitat and the breeding migrations of its fishes. Lake Turkana is at the precipice of large-scale changes in ecological function due to climate change and economic development along the Omo River, including the construction of massive dams and irrigation projects. Upstream development will reduce the volume of water entering the lake and dampen the lake's ecologically crucial seasonal flood pulse. These changes will almost certainly impact the lake's fisheries at a time when they are becoming increasingly important to local livelihoods and national food security. This dissertation considers how the lake's fish communities, which have not been well studied since the 1980's, will respond to upstream development. Using data from satellite altimetry and local fisheries organizations, this study showed that water levels and their fluctuations are key drivers of fisheries productivity in the system. Using geographic information systems, water levels were shown to alter the distribution of habitat types and seasonal flood pulses to determine the extent of productive dynamic littoral habitat in the lake. Stable isotope analysis and a breeding vulnerability index for the top fishery species in the system showed that while some species of economic importance are ecologically flexible (e.g. Oreochromis niloticus. Lates niloticus), others (e.g. Tilapia zillii, Labeo horie) are highly sensitive to changes in habitat availability and food web structure. Lastly, a synthesis of published food web models for African lakes showed that altering the magnitude of water level fluctuations of these lakes has implications for their productivity, fish diversity, and the complexity, efficiency and connectivity of their food webs. Taken together, these studies suggest that upstream development will have extensive negative consequences for Lake Turkana and its fisheries. Although recommendations are made regarding minimizing impacts to the lake, more research must be conducted to comprehensively inform water resource management in the region.

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