LE3 .A278 2015

2015

Avery, Trevor

Acadia University

Master of Science

Masters

Biology

Biology

Little Skate, Leucoraja erinacea, and Winter Skate, Leucoraja ocellata, are sympatric, sibling species in the western Atlantic Ocean. The K-selected life history characteristics of skates make them highly sensitive to exploitation, and long-term conservation efforts are required when populations have been overfished even if only as bycatch. Little Skate were assessed as Near Threatened, and Winter Skate Endangered in Canadian waters by the IUCN. Species identification is problematic in these species; therefore, sequencing of the mitochondrial DNA Cytochrome Oxidase I gene confirmed the identification of Little Skate and Winter Skate. Prior to 2013, skates had never been surveyed in the inner Bay of Fundy. Skates were sampled at an intertidal herring weir in Bramber, Nova Scotia, across three field seasons (2012 – 2014), and on directed trawls in the inner Bay of Fundy (2013 – 2014). In total, 2,396 skates were tagged and 135 skates were recaptured. Samples were collected for disc shape analysis using a General Procrustes Alignment, Procrustes ANOVA, and Principle Component Analysis. Of the skates genetically confirmed to species, it was found that trawling caught seemingly more Little Skate, while the weir caught more Winter Skate. Females outnumbered males across all seasons and both fishing methods. Small and medium-sized skates were most abundant across all years, and the greatest proportion of large individuals was at the start of the fishing season, in early May. Catch abundance appeared lowest at pre-neap and neap tides, and appeared greatest at approximately mid-amplitude tide height of -6 m on descending tides. A Schnabel population estimate of 29,465 (24,890 – 36,100) was calculated for likely local populations of Little Skate and Winter Skate, and most recaptured skates returned to the weir within 50 days. Estimates of sexual maturity for Little Skate and Winter Skate in the inner Bay of Fundy were 40 cm and 49 cm, respectively. Sexual dimorphism in disc shape was found in Little Skate, but not Winter Skate. Disc shape, clasper length, alar thorns, midline thorns, cloacal rough patch, and extruded cloacas are all useful for in-field species identification, particularly at 35 – 50 cm. Eyespots were found to not be indicative of species.

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https://scholar.acadiau.ca/islandora/object/theses:381