Science, as in life, does not always go to plan: where did all the sharks go?

Usually, research experiments and sampling designs are planned based on long-term knowledge. Data on species abundance, seasonality, and area preference are taken into consideration to decide where, when, and how to proceed. So, you plan ahead, you check everything, but, environmental conditions cannot be controlled and the year you choose to perform your science is different from the previous ones; summer is too hot, or too cold, it rains too much or too little, and the presence of your study species is affected.

This is exactly what happened to us. Our project aims at investigating the effects that pollutants have on the health status of three threatened shark species, two smooth-hounds (Mustelus mustelus and M. punctulatus) and the spiny dogfish (Squalus acanthias). In the area of the northern Adriatic Sea, information gathered from fishers’ local ecological knowledge and confirmed by preliminary acoustic telemetry data highlights that these species present seasonality, philopatry, and migratory pattern linked to temperature preference. Smooth-hounds migrate northwards in the basin during spring to give birth and reproduce along the Italian coasts. Contrarily the more mobile spiny dogfish prefer lower water temperatures and is more present during cold months. However, this was a particularly hot winter and smooth-hounds modified their movement pattern, postponing their migration towards the study area. Similarly, spiny dogfishes were not commonly present either. These conditions made finding sharks extremely challenging.

A common smooth-hound (Mustelus mustelus) being released at sea after tagging. Photo © Licia Finotto

But, hey, no problem, as a scientist you should always have a plan B. We were ready to modify our schedule and sample sharks as soon as they would have made their appearance. Unfortunately, when it rains, it pours! This year, winter and spring were not only unusually warm, but also unusually rainy. The high input of nutrients carried by rivers, associated with the warm temperatures, caused a bloom in microalgae populations and large mucilage aggregates started appearing. While sharks were not bothered by these giant green “dementors”, fishers struggled quite a lot. Since ours is a destructive sampling, we rely on animals captured by fishers to be sold at the fish market. Therefore, because no fisher went out at sea, we were unable to source all the samples needed.

A fisher explaining sharks’ movements in our study area. Photo © Licia Finotto

However, the time we spent onboard fishing vessels was not wasted. Not only did we get to soak in the beauty of nature and release some healthy sharks back at sea, but we could chat at length with fishers. We strengthened our collaboration and gained precious information on shark movements, distribution, and past abundances. We also took the chance to inform fishers about sharks’ high vulnerability and the severe threats they are facing. This is extremely important as fishers’ engagement in the cause is a fundamental key to successful conservation stories.

Environmental conditions are now favourable, and we are ready to jump on board and are hopeful of collecting many samples in the next months.