South American sea lions foraging Uruguay

Federico Riet Sapriza, Proyecto Pinnípedos

Resource competition between fisheries and marine mammal continue to raise concern worldwide. Understanding this complex conflict requires data on spatial and dietary overlap of marine mammal and fisheries. In Uruguay, the South American sea lions population has been dramatically declining over the past decade. The reasons for this population decline are unknown but may include the following: (1) direct harvesting; (2) reduced prey availability and distribution as a consequence of environmental change; or (3) biological interaction with fisheries. This study aims to determine resource overlap and competition between South American sea lions (SASL, Otaria flavescens, n=10) and the artisanal fisheries (AF), and the coastal bottom trawl fisheries (CBTF). We integrated data on sea lions diet (scat analysis), spatial and annual consumption estimates; and foraging behavior-satellite-tracking data from lactating SASL with data on fishing effort areas and fisheries landings. We found that lactating SASL are benthic divers and forage in shallow water within the continental shelf. SASL's foraging areas overlapped with CBTF and AF fisheries operational areas. Dietary analysis indicated a high degree of overlap between the diet of SASL and the AF and CBTF fisheries catch. The results of our work show differing degrees of spatial resource overlap with AF and CBTF, highlighting that there are differences in potential impact from each fishery; and that different management/conservation approaches may need to be taken to solve the fisheries-SASL conflict.

In this study we hypothesized that the biological interaction between SASL and fisheries may create sub-optimal foraging conditions for lactating females breeding in Isla de Lobos the second largest breeding colony. The objectives of the present study were as follows: (i) to examine the diving behavior of lactating SAS, (ii) to determine the spatial distribution of foraging effort of lactating SASL, (iii) to study the diet of lactating SASL, and (iv) to integrate these data with information of spatial distribution of fishing catch and effort to quantify the trophic and spatial overlap between SASL and the Uruguayan artisanal and coastal bottom trawl fisheries.

This research was funded by the US Marine Mammal Commission under the Grant no. E4047335 and the Office of Naval Research Grant N00014-08-1-1195, the E&P Sound and Marine Life Joint Industry Project of the International Association of Oil and Gas Producers.


We would like to thanks Nelson Veiga, José Luis Veiga, Gabriel Pereyra, Leonardo Olivera, D.J. Shuman, H. Katz, R. Frau, S. Tavoni, M. García, M. Rivas for their invaluable assistance and collaboration during the field work. We are also thankful to C. Leiza (Parque Zoológico Lecoq, Uruguay) for providing tranquilizing darts dart, and the Marine Mammal Center (Sausalito, California, USA) for lending the capture nets. We would like to acknowledge the logistical support of DINARA. The present work was conducted under the permit #572/208 approved by DINARA (National Administration of Aquatic Resources), Ministry of Livestock, Agriculture and Fisheries, Uruguay.

Overview

This section explains attributes included in the original dataset. OBIS-SEAMAP restricts the attributes available to the public to date/time, lat/lon and species names/counts only. Should you need other attributes described here, you are encouraged to contact the data provider.

Attributes described below represent those in the original dataset provided by the provider.
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Attributes in dataset

Attribute (table column)	Description
oid	Unique id (created by OBIS-SEAMAP)
obs_date	Observed date
obs_time	Observed time
latitude	Latitude
longitude	Longitude
series	Animal ID
device	PTT
device_id	PTT #
sex	Sex of animal tagged
age	Age of animal tagged
sp_obs	Species tagged
sp_tsn	Species ITIS TSN
obs_count	Observed count of tagged animal = 1