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Ecology

Digitally partnering with spearfishers to survey fish communities

 

Bulleri, F.; Benedetti-Cecchi, L. Chasing fish and catching data: recreational spearfishing videos as a tool for assessing the structure of fish assemblages on shallow rocky reefs. Marine Ecology Progress Series 506: 255-265, 2014. doi: 10.3354/meps10804

 A picture is worth a thousand words

Schutte 9.29

Why we care

Spearfishing videos yielded results that were not significantly different from those obtained from underwater SCUBA surveys, indicating that videos can be used as an alternative census method. These videos were used to determine the number of fish present in a specific location and whether a species of interest was present at a particular site. This is the first formal evaluation of species occurrence data gathered from spearfishing videos, which are not a citizen science tool currently being used by scientists.

Scientists: don’t forget that even the unlikeliest citizens may contribute to your science. Spearfishers may harvest some of the organisms that marine scientists study, but they could still provide valuable data at a fraction of the cost it would take to gather that data otherwise.

Non-scientists: a quick internet search will lead you to citizen science organizations in your area of interest that could benefit from even a little of your time. If you’re not sure where to start, check out these great resources: ZooniverseScientific American, Wikipedia.

Or contact a grad student near you if you’d like to volunteer in the lab or in the field- we’d love to have you join us!

Background

One of the biggest questions underlying the entire field of ecology is “why are species where they are?” For example, pollution impacts or competition between similar species may partly explain why species are present in some areas and not in others.

Schutte 9.29_1

A spearfisher waiting on the bottom for a target fish to come close.

However, it is often difficult to determine which species are where. Scientists have limited time and resources and cannot visit every site on Earth and record which species they see. In addition, shy and rare species pose their own challenges- if creatures hide or flee when humans are near or if they are so sparse that you have to be very lucky to see one, how can you know how many of that species there are in an area?

Scientists are increasingly turning to citizen science initiatives to obtain species occurrence data. Citizen scientists are not scientists by trade but they participate in either data collection or analysis. Marine scientists are working with citizen scientists to record shark sightings, explore the world’s deep oceans, map the spread of invasive species, and even clean up our oceans.

Because marine species are often surveyed using a wide variety of census methods, each with their own pros and cons, citizen science species sightings can contribute quality data to scientists who want to know which species are where. Spearfishing videos are currently not used for data collection efforts, and this study evaluated whether they could be.

Methods

Schutte 9.29_2

A still from a spearfishing video showing the type of sit and wait footage that the researchers were working with. Notice the number of non-target fish in the frame.

To directly compare the results of spearfishing videos to underwater censuses, the study’s authors performed transects to survey fishes while on SCUBA and in the same day, also conducted several mock spearfishing dives. They did this at 2 sites in northwestern Italy on 3 non-consecutive days.

Spearfishing videos are typically recorded on a small camera mounted on the gun or on the fisherman’s head. The method typically used to fish in the Mediterranean is what makes data gathering possible: fishermen settle onto the bottom, sometimes even hiding behind natural features on rocky reefs, and then wait for a target fish to swim close before attempting to spear it. While they are waiting on the bottom with their video camera recording, non-target fish are swimming into the frame and can be identified and counted. 150 m of transect data collected while on SCUBA were compared to data from 3 – 4 videos of spearfishing dives- enough to approximately duplicate the area surveyed by SCUBA divers.

Results

Species occurrence data are difficult to analyze statistically- if you didn’t see a species during a particular count, is it because it wasn’t there or because you didn’t see it? The researchers used models to estimate the error when using spearfishing videos and when counting fish on SCUBA. Fish counts from the two methods overlapped within their margin of error for the number of species seen per unit effort. This means that as long as enough spearfishing videos are analyzed, fish counts returned should be similar to those obtained using SCUBA counts.

Schutte 9.29_3

Model results showed overlap between the number of fish seen during underwater video counts (UVC) using SCUBA and in spearfisher videos.

This similarity between methods held for the presence or absence of a particular species of interest, but it did not apply to community composition- the percentage of a fish community made of each species seen there differed between the two methods. Both SCUBA censuses and video footage each returned the presence of several species (5 and 4, respectively) that were not seen at all during fish counts made using the other method.

One advantage of using spearfishing footage is that a single fisherman typically makes multiple dives within several hours, each to a different location within a site. Rather than using footage from a single point to obtain fish community information, scientists are then able to compile site information from multiple locations (mimicking SCUBA survey data compilation).

Spearfishing videos may also be useful for scientific endeavors because professional spearfishers typically hold their breath while underwater, eliminating the noise and bubbles present while SCUBA diving. This may encourage detection of shy species that may hide or flee in the presence of divers on SCUBA.

This type of recreational video offers another advantage that some citizen science data do not: because all the information is recorded on video, researchers can extract as much information from a video as they want. For example, footage could be used to assess habitat condition, percent cover of plants, presence of invasive species, or range expansion due to climate change in addition to fish occurrence data like that analyzed here.

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