419 American Fisheries Society Symposium 64:419–428, 2008 © 2008 by the American Fisheries Society Natural Hazards, Stock Depletion, and Stock Management in the Southern Gulf of Mexico Pink Shrimp Fishery FRANCISCO ARREGUÍN-SÁNCHEZ*, MAURICIO RAMÍREZ-RODRÍGUEZ, MANUEL J. ZETINA-REJÓN, AND VICTOR H. CRUZ-ESCALONA Centro Interdisciplinario de Ciencias Marinas del Instituto Politécnico Nacional Apartado Postal 592, La Paz, Baja California Sur, México Abstract.—The southern Gulf of Mexico has historically sustained important fish- eries, particularly shrimp. From the mid-1950s to early 1970s, annual yields of shrimp averaged about 27,000 metric tons (mt), of which the pink shrimp Farfantepenaeus du- orarum contributed more than 80%. At that time, three fleets, from the United States, Cuba, and Mexico, exploited the stock. Pink shrimp captures have declined from the mid-1970s to the present level of about 1,000 mt per year, indicating severe stock deple- tion. A monotonically decreasing recruitment rate, beginning in the early 1970s, was identified through reconstruction of the stock, based on age-structured analysis. At the beginning of the 1980s, total fishing effort decreased more than 40% because U.S. and Cuban fleets retired from this fishing ground, and about 50% of the Mexican fleet stopped operations because boat ownership was transferred from the private sector to fishing cooperatives. During this time, recruitment continued decreasing but at a slower rate. Because of the high yields obtained during the 1950s and 1960s, depletion was interpreted as caused by overfishing, especially since juveniles had been intensively exploited in coastal areas. Another hypothesis to explain the drop in recruitment was the start of oil industry operations in the 1980s; this theory was subsequently discarded because the recruitment rate reduction started in the early 1970s. In addition to the Ixtoc I oil spill in 1979, several natural events during the 1980s and 1990s coincided with the decrease in recruitment rate, including three high-impact hurricanes. Also, during this time, ash ejected by the Chichonal volcano covered large expanses of coast- al sea grasses, which serve as shrimp nursery areas. Using trends in recruitment rate anomalies, we identified recruitment failures caused by these natural hazards, but the time series showed that once the effect was removed, the pink shrimp stock responded towards recovery, so these events alone do not explain the stock depletion. Recruit- ment anomalies were strongly associated with changes in regional primary production, and both series showed a negative shift in the mid-1980s. We concluded that there are two time frames—short-term impacts caused by hurricanes, the volcanic eruption, and even oil spills; and a long-term effect associated with decreasing primary produc- tion. We found that this long-term effect is heavily influenced by related environmental changes, such as increases in water level and temperature, a decrease in salinity, the low intensity of turbulence in this area, the absence of river discharges that promote prima- ry production, and the low-energy hydrodynamics of the southern Gulf of Mexico. We suggest that the decrease in recruitment rate was strongly influenced by a decrease in salinity and the decrease in primary productivity, which is the main source of food for the shrimp. This discovery changed the objectives of management policy. Previously, the main objective was stock recovery, but now management policy is aimed at stock maintenance, especially of reproductive females, while waiting for a favorable change in productivity levels. * Corresponding author: francisco.arreguinsanchez@ gmail.com