Fisheries Research 100 (2009) 191–199 Contents lists available at ScienceDirect Fisheries Research journal homepage: www.elsevier.com/locate/fishres Improving management advice through spatially explicit models and sharing information Carlos Montenegro a,∗ , Mark N. Maunder b , Maximiliano Zilleruelo a a Instituto de Fomento Pesquero, Evaluacion de Recursos, Blanco 839, Valparaíso, Chile b Inter-American Tropical Tuna Comisión, 8604 La Jolla Shores Drive, La Jolla, CA 92037-1508, USA article info Article history: Received 23 April 2009 Received in revised form 23 July 2009 Accepted 24 July 2009 Keywords: Fisheries management Heterocarpus reedi Shrimp Spatial model Stock assessment abstract Recent assessments of Chilean shrimp, Heterocarpus reedi, in central Chile have been conducted separately for the northern and southern zones of the fishery and treating them as two separate stocks. However, it is not clear whether H. reedi of the two zones interact with one another or whether they share similar characteristics. Such knowledge is necessary to determine whether they should be modeled as separate “stocks” or as a single stock. This has motivated the use of the Pella–Tomlinson model to test whether there are spatial differences in the population dynamics of H. reedi in the two zones and whether sharing information between the zones improves management advice. We test if it is better, from a stock assess- ment point of view, to model the stock as one unit in the whole area, or as two separate stocks. In the single-stock model, we sum the catch data of both zones, but each catch-per-unit-of-effort index is fit as a separate data set, using a joint likelihood. Under the single-stock hypothesis, the best model fit was the symmetric production function (i.e. the Schaefer model for which the biomass that supports maximum sustainable yield as a proportion of carrying capacity (B MSY /B 0 ) = 0.5), with different catchability coeffi- cients for each CPUE index, but a shared standard deviation of the log-normal likelihood function. Under the two-stock hypotheses, both catch and CPUE data were separated for each zone in the model. In this case, the best model fit is also the one with symmetrical production curve, and the only parameter that differed between the zones was B 0 . However, B 0 per unit of habitat was similar for the two zones. Also, the precision of estimated management quantities was improved by modeling the appropriate spatial structure and sharing information among zones. The results suggest that the demographic parameters are similar for the two zones. It appears that the main difference between the two zones is the exploita- tion history, with the catch in the southern zone being reduced earlier than in the northern zone and consequently the biomass in the southern zone increased earlier than in the northern zone. This implies that local depletion can occur in this stock and that differences in management among zones may require explicitly modeling sub-stocks in the assessment of this and other species. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The Chilean shrimp (Heterocarpus reedi, Decapoda, Pandalidae) has a wide distribution off the coast of Chile. It inhabits the bot- tom of the continental shelf and upper slope from about 21 ◦ 30 ′ S to about 38 ◦ 43 ′ S, at depths between 150 and 600 m. Commer- cial exploitation started during the 1960s, making it one of the oldest crustacean fisheries in Chile. The fishery extends between region II and region VIII (Region de Atacama to Region del Bío Bío), but the main fishing grounds are located between 27 ◦ S and 37 ◦ S (Region III to Region VIII). The fishery administration (Subsecre- tariat of Fishery) declared the fishery to be fully exploited in 1995, ∗ Corresponding author. Tel.: +56 32 2151404; fax: +56 32 2151645. E-mail address: cmontene@ifop.cl (C. Montenegro). and established a total allowable catch quota of 10,000 t for 1996. Spatially, the management of the resource is based on two main zones: the northern zone, from latitude 26 ◦ 03 ′ S to 32 ◦ 12 ′ S (includ- ing Regions II to IV), and the southern zone, from latitude 32 ◦ 12 ′ S to 38 ◦ 28 ′ S (Regions V to VIII, Fig. 1). As landings showed a precipitous decrease during 1997–2000, individual quotas were introduced in 2001 and the total catch quota was split in a temporal and spatial fractioning that included the complete closure of the southern zone. Since then, alternate closures to regions in the southern zone have been applied annually, while a total catch quota has been main- tained at around 5000 t/year. The landings have been around 80% of total catch quota with a total of 4215 t in 2006 and 4340 t in 2007. No spatial restrictions have been applied since 2006. The manage- ment of the fishery includes annual stock assessments to estimate the status of the resource, analyze the implications of different management actions, and determine the total allowable catch. 0165-7836/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2009.07.006