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Collaborative Research and Data-Limited Assessment of Small-Scale Trap Fisheries in the Santa Barbara Channel


Globally, most fisheries are managed ineffectively. Model-based stock assessments that estimate biomass-based reference points work well for sustainably managing data-rich fisheries, but small-scale fisheries typically lack the data and/or resources needed to perform these assessments. These fisheries comprise the majority of fisheries worldwide, and they require alternative monitoring and assessment methods to better understand fishing’s impact on targeted populations and to enhance the sustainability of fished stocks. In this dissertation, I focus on the application of alternative monitoring and assessment techniques to improve understanding and management of two invertebrate fisheries in the Santa Barbara Channel (SBC) in southern California (CA).

The first two chapters focus on the multispecies southern CA rock crab fishery, which experienced rapid growth from 2010 to 2015 in the SBC. However, rock crab stock health has never been assessed because substantial biological data limitations exist, species-specific catch data is often unreported, and effort data is not available in this fishery. In the first chapter, I performed five data-limited assessments in an effort to identify any early warning signs of depletion in the fishery. Methods selection was supported by novel decision support software (FishPath) designed to facilitate the selection of context-appropriate assessment and management options for coastal fisheries. Expert opinion of stakeholders was vital when interpreting the suite of assessment results, which suggested that the rock crab fishery may be experiencing serial depletion, effort creep, and regional overfishing. The approach taken delivers a widely applicable means for improving understanding of fishery impacts in data limited circumstances, and I suggest a proactive management strategy to address warning signs of overfishing for southern CA rock crab.

In chapter two, I employed a collaborative approach to further assess these early warning signs of overfishing. The rock crab fishery is managed as one assemblage despite life history differences across species and space, as well as spatial variation in fishing effort and species composition of the catch. Uniformly managing such a complex system renders it difficult to assess which rock crab stocks are most affected by the increased fishing pressure in the SBC. I tested for stock-specific declines by replicating a 2008 study in 2016-17, where local fishers collected key fishery-dependent indicator data across the SBC and I compared indicator values between studies. Spatially explicit multiple regression analyses revealed significant declines in male crab sizes, overall CPUE, and the proportion of crab retained (versus discarded) for all heavily targeted stocks. Evidence of decline varied with species, location, and sex, but overall, fishers caught fewer pounds of crab per trap in 2016-17 than in 2008. This work provides a foundation for an adaptive, spatially explicit, empirical management strategy for southern CA rock crab, which may help fishers to avoid financial loss and further depletion of certain stocks. It also demonstrates that relatively simple collaborative approaches can provide valuable insight into complex fishery systems in need of improved management.

In chapter three, I focus on the use of no-take marine reserves as a tool for fisheries management. Marine reserves are a widely used and successful strategy for conserving biodiversity, but their ability to benefit adjacent fisheries through spillover of larvae, juveniles, and adults is often uncertain. Assessing fishery-related benefits of individual reserves requires careful evaluation on a case-by-case basis. This chapter examines spillover contributions from a no-take marine reserve network established in 2003 at the Northern Channel Islands, CA to the southern CA spiny lobster (Panulirus interruptus) fishery. Collaborative fisheries research (CFR) in 2006-08 found considerable population increases within these reserves and potential spillover across reserve borders. I replicated the 2006-08 effort in two reserves in 2018 to quantify further accumulation of biomass inside the reserves, and to test whether spillover led to increased trap yield outside reserve borders following 15 years of reserve protection. The study design controlled for individual reserve characteristics, fisher behavior, and environmental conditions. I found that catch per trap increased 125–465% deep within reserves, 223–331% near outer reserve boundaries, and did not increase at control sites. Spillover therefore contributes to enhanced catch for the Southern CA spiny lobster fishery, and this study illustrates the utility of CFR for assessing the effectiveness of marine reserves as fishery management tools worldwide.

As a whole, this dissertation exemplifies the use of collaborative, alternative approaches to stock monitoring and assessment that can be applied to improve the management of small-scale fisheries worldwide.

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