Dissertation

Lagged Recruitment, Indirect Interactions, and Delayed Recovery in Multi-Species Fisheries

Aalto, Emilius August

2013

Overview

Ecosystem-based fisheries management must consider many elements of a complex marine community and, to accurately model the abundance of a particular target species, it is necessary to determine the most important out of many possible ecological dynamics. Here we consider three potential drivers: temporal heterogeneity, non-target effects, and species interactions. Firstly, we investigated how the assumption of equal recruitment and mortality timing, common to many fishery production models, affects stock estimates for data-poor species. Adjusting models to include no mortality delay and a recruitment time lag equal to age-at-maturity eliminated a 14-40% over-estimation of overfishing limits. Estimation error increases with age-at-maturity and natural mortality rate, indicating that time lag separation is most important for long-lived species. Secondly, we analyzed the balance within a multi-species fishery between non-target bycatch and positive indirect interactions between species. If the species involved interact strongly, the release from competition or predation can counteract or exceed the negative effects of bycatch. In particular, in communities where a shared predator forms a strong link between the target and non-target species, the positive effects of release from apparent competition can be larger than those of direct competitive release. Finally, we explored how the presence of an obligate predator affects recovery trajectories in the post-harvest period of a target species with a truncated size distribution. Compared to generalist predation, obligate predation delays the recovery of large prey individuals to pre-harvest abundance, even for sizes not targeted by the predator. In addition, the obligate predator lowered the relative abundance of smaller vulnerable individuals, delayed the shift to pre-harvest size distribution, and complicated post-harvest monitoring through population cycling. We conclude that the use of appropriate life-history time scales and the inclusion of strong species interactions are both important aspects of fisheries management, and their omission can cause over-estimation of initial stock size, damage from bycatch, and species recovery potential. Keywords Fisheries management; time lags; delayed recruitment; mortality; density dependence; stock assessment; Depletion-Based Stock Reduction Analysis.

• Publisher: ProQuest Dissertations & Theses
• Subject: Aquatic sciences / Ecology / Environmental science
• ISBN: 1303441993, 9781303441998