Ecological Modelling 221 (2010) 919–926 Contents lists available at ScienceDirect Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel A simulation model to explore the relative value of stock enhancement versus harvest regulations for fishery sustainability Mark W. Rogers a,∗ , Micheal S. Allen a , Paul Brown b , Taylor Hunt b , Wayne Fulton b , Brett A. Ingram b a School of Forest Resources and Conservation, The University of Florida, 7922 NW 71st Street, Gainesville, FL 32653, United States b Department of Primary Industries, Marine and Freshwater Fisheries Research Institute, Goulburn Valley Highway, Snobs Creek, Private Bag 20, Alexandra, VIC 3714, Australia article info Article history: Received 29 July 2009 Received in revised form 14 December 2009 Accepted 18 December 2009 Available online 14 January 2010 Keywords: Stock enhancement Fisheries sustainability Harvest abstract Harvest restrictions and stock enhancement are commonly proposed management responses for sus- taining degraded fisheries, but comparisons of their relative effectiveness have seldom been considered prior to making policy choices. We built a population model that incorporated both size-dependent har- vest restrictions and stock enhancement contributions to explore trade-offs between minimum length limits and stock enhancement for improving population sustainability and fishery metrics (e.g., catch). We used a Murray cod Maccullochella peelii peelii population as a test case, and the model incorporated density-dependent recruitment processes for both hatchery and wild fish. We estimated the spawning potential ratio (SPR) and fishery metrics (e.g., angler catch) across a range of minimum length limits and stocking rates. Model estimates showed that increased minimum length limits were much more effective than stock enhancement for increasing SPR and angler catches in exploited populations, but length limits resulted in reduced harvest. Stocking was predicted to significantly increase total recruitment, population sustainability, and fishery metrics only in systems where natural reproduction had been greatly reduced via habitat loss, fishing mortality was high, or both. If angler fishing effort increased with increased fish abundance from stocking efforts, fishing mortality was predicted to increase and reduce the benefits real- ized from stocking. The model also indicated that benefits from stock enhancement would be reduced if reproductive efficiency of hatchery-origin fish was compromised. The simulations indicated that stock enhancement was a less effective method to improve fishery sustainability than measures designed to reduce fishing mortality (e.g., length limits). © 2010 Elsevier B.V. All rights reserved. 1. Introduction Sustainability of open-access recreational fisheries is an increas- ing concern in both freshwater and marine systems. There is growing evidence of overfishing from recreational fishing across broad spatial and temporal scales (Post et al., 2002; Cooke and Cowx, 2004). Limiting angler effort to reduce overfishing in pub- lic resource fisheries is difficult, therefore resource managers have often adopted aggressive management strategies such as stringent length limits and bag limits (e.g., walleye Sander vitreus in Wis- consin, Beard et al., 2003), and increased use of closed areas and seasons after contentious debates. Stock enhancement programs are often favored by angler groups for restoration and sustainability of fisheries that have undergone overfishing and/or loss in habitat ∗ Corresponding author. Tel.: +1 352 273 3651; fax: +1 352 392 3672. E-mail addresses: mrogers@ufl.edu (M.W. Rogers), msal@ufl.edu (M.S. Allen), Paul.Brown@dpi.vic.gov.au (P. Brown), Taylor.Hunt@dpi.vic.gov.au (T. Hunt), Wayne.Fulton@dpi.vic.gov.au (W. Fulton), Brett.Ingram@dpi.vic.gov.au (B.A. Ingram). quantity and quality (Grimes, 1998; Molony et al., 2003; Lorenzen, 2005). Despite positive intentions of stock enhancement programs, substantial evidence shows that stock enhancement can be inef- fective or cause harm to the fisheries which are targeted for improvement. Hilborn and Eggers (2000) showed that one of the world’s largest hatchery operations (i.e., pink salmon Oncorhynchus gorbuscha stocking in Prince William Sound) resulted in replace- ment of wild stocks rather than additive effects to natural recruitment. Lorenzen (2005) gave an overview of the potential benefits and pitfalls of stock enhancement and showed that stock- ing large, recruited fish can substantially increase fishery yields, whereas stocking maladapted hatchery fish can cause substan- tial negative impacts via introgression with native fish and reduce population abundance. Hilborn (1999) commented that responsi- ble use of hatcheries in management should focus on (1) testable objectives for the hatchery programs including a plan for evalu- ation of those objectives, (2) measures of survival of stocked fish via tagging programs and monitoring, and (3) an assessment of whether the hatchery program produces a net augmentation to the wild stock. Leber (2002) also called for thorough evaluation and 0304-3800/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2009.12.016