title: Distribution and habitat associations of deep-sea fishes in a marine protected area: the ecological role of soft-bottom biogenic habitats for groundfish populations in the northwest Atlantic, and implications for conservation
Creators: name: Boulard, Marion
Publisher: name: Museo Egizio
publisherIdentifier: https://ror.org/058zzep76
publisherIdentifierScheme: ROR
Year: 2024

description: While many studies have assessed relationships between fishes and large hard-substrate cold-water corals (CWC), relatively few have examined the relationships of fish with habitat provided by smaller corals in soft-bottom environments. Here, I analyzed data from two in-situ benthic surveys, collected in 2017 and 2018 by two underwater video systems (UVS) in the Laurentian Channel Marine Protected Area (MPA), which hosts the largest known sea pen densities and diversity in the Canadian Northwest Atlantic. My objectives were 1) to understand the small-scale linkages between fish, biological and physical habitat features in a soft-sediment deep-sea environment, and 2) to evaluate the bias and relative effectiveness of UVSs to bottom trawls in sampling fish assemblage characteristics. I found evidence of taxon-specific influence of specific habitat biotic and abiotic features on fish density, especially CWC habitats. Specifically, I suggest that sea pens in the Laurentian Channel MPA may provide nursery habitats for early-life stage fishes dominating the assemblage and that fish undergo ontogenetic shifts in micro-habitat use and specialization. Most taxa and fish did not react to UVSs or not enough to induce bias in estimating observed abundances, and variability in fish reaction was mostly influenced by fish in-situ behavior. In addition to improving UVS assessments, studying fish behavior – both in-situ and response – and its variability with ecological factors can improve our knowledge on fish habitat use and ecology. Additionally, I illustrate similar fish diversity and relative abundance (for a similar survey area covered), higher total and specific fish densities and similar fish population size structure assessed by UVS compared to that caught by scientific bottom trawls. Overall, my results suggest that: 1. Small-scale heterogeneity of specific biotic and abiotic habitat features in a soft-bottom environment has a taxon-specific influence on fish distribution. 2. Sea pens in the Laurentian Channel MPA provide safe resting and feeding grounds for early-life stage fishes that may stay over multiple years to grow before presumably migrating and settling in their adult habitat. 3. However, fish-habitat associations were not as strong as associations found in hard-bottom ecosystems, suggesting a facultative relationship between fish and invertebrates in the MPA. 4. Sea pens in the MPA should be protected as a habitat in addition to as a taxon, and monitoring indicators should include fish-related metrics. 5. UVSs have proven to be an efficient, non-destructive tool to yield in-situ small-scale distribution of fish in association with benthic habitat attributes, and in-situ imaging can be an effective alternative to scientific bottom-trawl surveys. This approach can meet long-term monitoring objectives of the Laurentian Channel MPA to assess fish populations.