Opportunistic observation effort and seasonal-spatial fidelity: a qualitative approach, applied to an Orcinus orca first record

Abstract

Abstract This study formulates a qualitative image-based approach to establishing cetacean sightings’ effort at an ecosystem scale in the Gulf of Maine. As a first step, I investigate a rare set of long-term sightings (2008–2017, the study period) of a male killer whale (Orcinus orca) representing unusually consistent occurrences, without considering observation effort. Largely unknown, killer whale populations in the NW Atlantic are tiny, travelling over vast areas, and at risk of human-caused extinction. The synthesis uses opportunistic observations, reported mainly by recreational mariners and commercial fishers incorporated into data manipulations anonymously. Adding an effort index using the qualitative image-based approach, I then investigate the hypothesis that the killer whale sightings constitute seasonal-spatial fidelity to the greater GoM, the first documentation of fidelity patterns in the western Atlantic hemisphere. The analysis includes comparisons to frequency distributions of single killer whales in the gulf in the historical past as a baseline, i.e. post mid 1940s. Finally, the fidelity analysis reveals a substantial spatial anomaly in the recent sightings data for the northeastern GoM. An explanation for the emergent anomaly is pursued by analyses of indicators of the availability of Atlantic herring (Clupea harengus) [fisheries landings, Atlantic puffin (Fratercula arctica) chick diets] as potential prey in the NE gulf. With the development of complementary corroborative approaches to the analysis of incidental sightings, it is possible to chip away at impediments to the understanding of ecosystem attractants and deterrents with respect to cetacean distributions.