Fishing during extreme heatwaves alters ecological interactions and increases indirect fishing mortality in a ubiquitous nearshore system

PURPOSE:
The data files contained herein are meant to serve as supplementary material for a published paper regarding the effects of clam digging during extreme heat waves on predator-prey interactions and indirect fishing mortality. This page will be updated with the complete citation for the article once it is officially published.
            

DESCRIPTION:
The increasing frequency and severity of heatwaves driven by global climate change are projected to have multifaceted ecological effects. While studies have assessed the impacts of heatwaves at the organism and population level, field-based studies documenting the effects of heatwaves on in situ ecological interactions are rare. Furthermore, studies assessing the biological and ecological implications of direct anthropogenic disturbance during heatwaves are absent. Here, we leverage mesocosm field experiments to document the effects of human activity (clam fishing) during an extreme heatwave on a ubiquitous predator-prey system at the land-sea interface: nearshore crabs and their bivalve prey. In monthly field experiments from May to September, we simulated clam fishing at low tide and subsequently returned marked, sub-legal sized clams to the sediment surface at three different tide levels; predator exclusion containers were used to protect half of the clams from crab predation. Reburrowing and mortality rates were recorded immediately after fishing and after 24- and 48 hours. Results showed that, typically, indirect fishing mortality was low and the vast majority of clams reborrowed within 24 hours. However, during an extreme heatwave in June, the clams appeared visually unhealthy during fishing and failed to reborrow, leading to near complete mortality during the heatwave. Estimates of predator activity were ≈5× higher during the heatwave compared to other months, and the majority of indirect fishing mortality was attributable to predation. When put into the context of air temperature thresholds, there was a clear shift after 30ºC, whereby clam reborrowing plummeted, and predator activity and mortality increased dramatically. Ultimately, our study provides strong field-based evidence that ecological shifts during heatwaves, facilitated by altered organismal physiology, can drive substantial indirect fishing mortality in a nearshore fishery where such mortality is otherwise low. These results not only provide support for climate driven alterations to predator-prey dynamics and ecosystem function but generate pertinent information for an ecosystem approach to fisheries management.
            

PARAMETERS COLLECTED:
Clam size (shell length)
Clam reborrowing rates
Clam mortality rates
Predator activity estimates
Air temperature

NOTES ON QUALITY CONTROL:
Data collected by Jeff Clements, Sarah Harrison, Mylène Roussel, Jillian Hunt, Brooke-Lyn Power, and Courtney Jones. Original data entry by Sarah Harrison. Data checked and validated prior to analysis by Jeff Clements. Data further checked and validated prior to publication by CADI.

PHYSICAL SAMPLE DETAILS:
No physical samples retained; all observations and counts conducted directly in the field.

SAMPLING METHODS:
i. Experimental fishing for soft-shell clams
ii. Experimental manipulation of crab access to clams (predator inclusion/exclusion experiments)
iii. Observations of clam burrowing behaviour and mortality
iv. Counts of predators and scavengers within experimental manipulations
v. Data mining air temperature (ECCC historical data website)

USE LIMITATION:
Please contact the data custodians before attempting to use this information in support of any kind of scientific analyses.

Organization: Fisheries and Oceans Canada | Pêches et Océans Canada