Using the Randomized Response Technique to Investigate Illegal Fishing and Contribute to Abalone Management in Northern California

<p>Illegal fishing has detrimental environmental and social impacts, but these effects are difficult to mitigate without reliable estimates of fisher non-compliance. Methods used by fisheries managers to estimate illegal fishing often require indirect estimation of poaching using biological, economic, or sociological indicators. This study presents a unique application of the randomized response technique (RRT) for direct estimation of non-compliance in the Northern California recreational red abalone (Haliotis rufescens) fishery. Using an anonymous paper-based compliance and sociodemographic survey of recreational fishers in Sonoma and Mendocino Counties, I estimate 29% non-compliance with the daily take limit, 23% with the minimum size limit, 19% with licensing laws, and 15% with the annual take limit and among the general population. No significant relationship between the socio-demographic variables gathered (age, income, county of residence, fishing experience) and RRT survey responses indicates that no clear profile can be ascertained to help identify potential violators. However, visitors have higher non-compliance estimates for all regulations except daily take limits, for which an estimated 72% of locals violate vs. only 18% of visitors. These rule-specific violation estimates allow for the development of efficient management priorities, as managers may target specific measures or user groups. Further research should develop quantitative RRT estimates of illegal take, and explore violation drivers operating within the fisher population.</p>

Using the Randomized Response Technique to Investigate Illegal Fishing and Contribute to Abalone Management in Northern California

<p>Illegal fishing has detrimental environmental and social impacts, but these effects are difficult to mitigate without reliable estimates of fisher non-compliance. Methods used by fisheries managers to estimate illegal fishing often require indirect estimation of poaching using biological, economic, or sociological indicators. This study presents a unique application of the randomized response technique (RRT) for direct estimation of non-compliance in the Northern California recreational red abalone (Haliotis rufescens) fishery. Using an anonymous paper-based compliance and sociodemographic survey of recreational fishers in Sonoma and Mendocino Counties, I estimate 29% non-compliance with the daily take limit, 23% with the minimum size limit, 19% with licensing laws, and 15% with the annual take limit and among the general population. No significant relationship between the socio-demographic variables gathered (age, income, county of residence, fishing experience) and RRT survey responses indicates that no clear profile can be ascertained to help identify potential violators. However, visitors have higher non-compliance estimates for all regulations except daily take limits, for which an estimated 72% of locals violate vs. only 18% of visitors. These rule-specific violation estimates allow for the development of efficient management priorities, as managers may target specific measures or user groups. Further research should develop quantitative RRT estimates of illegal take, and explore violation drivers operating within the fisher population.</p>

Survivors of Climate Driven Abalone Mass Mortality Exhibit Declines in Health and Reproduction Following Kelp Forest Collapse

Marine ecosystems are vulnerable to climate driven events such as marine heatwaves yet we have a poor understanding of whether they will collapse or recover. Kelp forests are known to be susceptible, and there has been a rise in sea urchin barrens around the world. When temperatures increase so do physiological demands while food resources decline, tightening metabolic constraints. In this case study, we examine red abalone (Haliotis rufescens) looking at sublethal impacts and their prospects for recovery within kelp forests that have shifted to sea urchin barrens. Abalone are a recreationally fished species that once thrived in northern California’s bull kelp forests but have recently suffered mass mortalities since the 2014–2016 marine heatwave. Quantitative data exist on the health and reproduction of abalone both prior to and after the collapse. The survivors of the mass mortality show a 2-year lag in body and gonad condition indices. After the lag, body and gonad indexes decreased substantially, as did the relationship between shell length and body weight. Production of mature eggs per female declined by 99% (p &lt; 0.001), and the number of eggs per gram of female body weight (2,984/g) declined to near zero (9/g). The number of males with sperm was reduced by 33%, and the sperm abundance score was reduced by 28% (p = 0.414). We observed that these reductions were for mature eggs and sperm while immature eggs and spermatids were still present in large numbers. In the lab, after reintroduction of kelp, weight gains were quickly lost following a second starvation period. This example illustrates how climate-driven declines in foundation species can suppress recovery of the system by impacting body condition and future reproduction of surviving individuals. Given the poor reproductive potential of the remaining abalone in northern California, coupled with ongoing mortality and low kelp abundances, we discuss the need to maintain the fishing moratorium and implement active abalone restoration measures. For fished species, such as abalone, this additional hurdle to recovery imposed by changes in climate is critical to understand and incorporate into resource management and restoration.

Hyperspectral interference tomography of nacre

Structural characterization of biologically formed materials is essential for understanding biological phenomena and their enviro-nment, and for generating new bio-inspired engineering concepts. For example, nacre—the inner lining of some mollusk shells—encodes local environmental conditions throughout its formation and has exceptional strength due to its nanoscale brick-and-mortar structure. This layered structure, comprising alternating transparent aragonite (CaCO3) tablets and thinner organic polymer layers, also results in stunning interference colors. Existing methods of structural characterization of nacre rely on some form of cross-sectional analysis, such as scanning or transmission electron microscopy or polarization-dependent imaging contrast (PIC) mapping. However, these techniques are destructive and too time- and resource-intensive to analyze large sample areas. Here, we present an all-optical, rapid, and nondestructive imaging technique—hyperspectral interference tomography (HIT)—to spatially map the structural parameters of nacre and other disordered layered materials. We combined hyperspectral imaging with optical-interference modeling to infer the mean tablet thickness and its disorder in nacre across entire mollusk shells from red and rainbow abalone (Haliotis rufescens and Haliotis iris) at various stages of development. We observed that in red abalone, unexpectedly, nacre tablet thickness decreases with age of the mollusk, despite roughly similar appearance of nacre at all ages and positions in the shell. Our rapid, inexpensive, and nondestructive method can be readily applied to in-field studies.

Evolved differences in energy metabolism and growth dictate the impacts of ocean acidification on abalone aquaculture

Ocean acidification (OA) poses a major threat to marine ecosystems and shellfish aquaculture. A promising mitigation strategy is the identification and breeding of shellfish varieties exhibiting resilience to acidification stress. We experimentally compared the effects of OA on two populations of red abalone (Haliotis rufescens), a marine mollusc important to fisheries and global aquaculture. Results from our experiments simulating captive aquaculture conditions demonstrated that abalone sourced from a strong upwelling region were tolerant of ongoing OA, whereas a captive-raised population sourced from a region of weaker upwelling exhibited significant mortality and vulnerability to OA. This difference was linked to population-specific variation in the maternal provisioning of lipids to offspring, with a positive correlation between lipid concentrations and survival under OA. This relationship also persisted in experiments on second-generation animals, and larval lipid consumption rates varied among paternal crosses, which is consistent with the presence of genetic variation for physiological traits relevant for OA survival. Across experimental trials, growth rates differed among family lineages, and the highest mortality under OA occurred in the fastest growing crosses. Identifying traits that convey resilience to OA is critical to the continued success of abalone and other shellfish production, and these mitigation efforts should be incorporated into breeding programs for commercial and restoration aquaculture.