MEPS 620:15-32 (2019)  -  DOI: https://doi.org/10.3354/meps12978

ABSTRACT: Every summer, endangered leatherback sea turtles Dermochelys coriacea migrate to temperate Atlantic Canadian waters to feed on gelatinous zooplankton (‘jellyfish’). Jellyfish distributions often seem episodic, making them difficult to survey over broad scales. We use a citizen science approach to track spatio-temporal patterns and environmental drivers of jellyfish occurrence, and ask how this dynamic prey field shapes leatherback sea turtle distribution in Atlantic Canadian waters. A total of 104 citizen scientists completed weekly beach surveys over 6 years, observing >23600 stranded jellyfish. We used these observations to describe jellyfish phenology. Cyanea capillata was the most commonly detected species (75.5% of all species-specific sightings), with peak temporal occurrence in July and peak spatial occurrence in the Gulf of St. Lawrence. Generalized linear modelling indicated that sea surface temperature and observer effort were significant positive predictors of C. capillata shoreline strandings. Leatherback presence was assessed by opportunistic observer sightings and cross-referenced with satellite telemetry data. Leatherback seasonality generally tracked jellyfish occurrence in Atlantic Canadian waters. On the Scotian Shelf, turtle distributions derived from historical and concurrent leatherback satellite telemetry and opportunistic sightings data lagged peak jellyfish occurrence by 2 wk; however, the pattern of relative timing was less clear during extensive turtle residency in the Gulf of St. Lawrence. These findings suggest that observations by the general public represent an important contribution to tracking the spatio-temporal distributions of jellyfish and that this information is useful in predicting dynamic habitat use for the endangered leatherback turtles that prey on them.

KEY WORDS: Gelatinous zooplankton · Jellyfish · Citizen science · Cyanea capillata · Dermochelys coriacea · Predator-prey relationship