Scientists need to count fish accurately to understand how fisheries and environmental change affect stocks over time. That is no easy task. As fishery scientist John Shepherd once said: “counting fish is like counting trees, except that they are invisible and they keep moving!” One way to count fish is to use cameras that can survey a wide range of depths. These cameras use parallel laser beams that are 10 centimetres apart. The laser beams project as dots on the seafloor or on fish, and the known distance between the dots provides a scale for estimating the size of the fish, of habitat features like boulders and corals, and the width of the survey transect.
One problem is that some fish species may chase the lasers dots and be drawn into the camera frame from somewhere to the side, which could bias the counts towards those species.
This problem got Twyla thinking, and she turned it into her 2017 science fair project.
In 2015, IPS student, Twyla had spent a week living out of Wuikinuxv Village, in River’s Inlet, helping members of the Wuikinuxv First Nation and her dad, Alejandro, who is an ecologist and science coordinator for the Central Coast Indigenous Resource Alliance, conduct camera surveys of fish. For her project, Twyla analyzed the video footage from those surveys, determining which species of fish chased the laser dots and which species did not. Through discussions with Alejandro, she began to wonder whether fish perceive the approaching camera as a threat, and the laser beams, which move as dots along the bottom, as potential prey. Consistent with that hypothesis, and building on the history of scientific ideas about animal behaviour, the results showed that fish species with relatively short lifespans—such as lingcod and kelp greenling, which are risk-takers that prioritize finding food and reproducing in the short-term—were most likely to follow the laser dots. In contrast, rockfishes that live a century or more, and which take less risks to find a short-term meal and prioritize staying alive to reproduce every year of their long adulthood, were less likely to follow the laser dots. These effects were strongest for species that feed on prey that move along the bottom, but weakened when fish were in the safety of larger groups.
In 2018, Alejandro worked with a colleague, Madeleine McGreer, to refine the analyses started by Twyla, and developed a method that used the results to correct for biased fish counts. The study, Chasing the light: Positive bias in camera-based surveys of groundfish examined as risk-foraging trade-offs, is now published in the international scientific journal Biological Conservation (available at https://authors.elsevier.com/a/1YRTv1R~eAu19), with Twyla as a coauthor.
The IPS community was also fortunate to have Twyla and Alejandro present at a recent Community Faculty event.