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American Fisheries Society 144th Annual Meeting

August 17-21, 2014
Quebec City, Canada


Dr. Ellen Pikitch Receives The 2014 American Fisheries Society Award for Excellence in Public Outreach

IOCS Presentations

Natasha Gownaris and Ellen K. Pikitch, "Diet Flexibility As an Indicator of Resilience in Lake Turkana, Kenya Fish Communities," Thursday, August 21, 2014: 10:50 AM.


Lake Turkana, Kenya, is the world’s largest desert lake and is fed primarily by the Omo River in Ethiopia. Dam and irrigation development will alter the Omo River’s flow patterns over the coming decade, with implications for the lake’s ecological functioning. Despite the importance of the lake’s fishes to the region’s wildlife and tribes, the ecosystem is remarkably understudied. Our work aimed to predict how resilient Lake Turkana’s fish communities are to perturbation based on the incidence of diet flexibility. We collected fish tissue samples from Lake Turkana (2008-2013) and analyzed them for δ­13C and δ15N. We compared isotopic niche variables (e.g. SIBER, bootstrapped Layman’s Metrics) among 8 key species, chosen based on economic or ecological importance and to represent all trophic guilds in the ecosystem. Among the 8 species studied, isotopic niche size varied by a factor of 2 and a priori factors (i.e. site, site, and year) explained approximately 50% of isotopic variability. Measures of intra-species dispersion in isotopic signatures supported these findings, indicating higher trophic diversity among species with larger isotopic niches. Based on these data, we conclude that diet flexibility is most marked in Nile tilapia and least marked in characids and Tigerfish in this system.

Konstantine J. Rountos and Ellen K. Pikitch, "Are We Catching What They Eat? - Assessing Mean Trophic Level of Fisheries Catch and Predator Consumption Globally," Thursday, August 21, 2014: 1:30 PM.


The mean trophic level of fisheries catch (mTLY) is commonly used as an index to evaluate the state of fisheries in ecosystems. Here, it was used simply to estimate the mean trophic level of catches for 1) all fisheries, 2) all finfish fisheries, and 3) all forage fisheries. In a similar manner, the mean trophic level of predator consumption (mTLq) index was used to estimate the trophic level of prey items that marine predators were consuming in a given ecosystem. These indices were used in order to screen for potential ecosystems or latitude groups where fisheries and the major predator categories (i.e. seabirds, marine mammals, and large predatory fish) may be targeting prey at similar trophic levels. We utilized 43 marine ecosystem models (Ecopath) from an existing database and from other sources, which represented ecosystems within the last 40 years and included all the major predators groups. Few differences were found between the mean trophic levels targeted by fisheries and predators, and no differences were found between forage fisheries and predators on latitudinal scales. Our results show where potential conflicts for forage species may arise between these ecological stakeholders, providing information that can inform an ecosystem-based approach to management.

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