Finding Game Fish with help from the CSIRO
Wade Whitelaw, Jock Young, Tim Lamb and Russell Bradford from the CSIRO Division of Fisheries recently under took some fisheries research with the help of recreational anglers. This report from them is reproduced in part from, and with permission from Gil Schott's excellent magazine Saltwater Fishing - Issue 5. Available at all good Newsagents.
Why are fish where they are when they are?
Understanding the factors affecting the distribution and movement of fish species is a major focus of fisheries research today and has many implications for fisheries management. However, to understand why fish are where they are when they are is a costly and time consuming process, usually because such research needs to be carried out over large distances with limited resources.
So, how can one obtain an "˜oceanographic snapshot"of an area and link this information to what is being caught. The Easter 1995 game fishing tournament hosted by the St. Helens Game Fishing Club at St Helen's was an opportunity for us to harness the enthusiastic assistance of game fish fraternity to help us obtain a better understanding of the association between fish and the water their habitat.
Over two days more than 40 competitors and their boats cooperated in a pilot recreational fishing research project. The competitors ranged across 700 square miles of ocean and they studiously recorded the species of fish they caught, their locations, water temperatures and overall catch weights. This information was then entered on to CSIRO's existing database and we now have a more complete picture of an expanse of ocean on which many anglers pin their hopes every year.
The spirit of cooperation
Recreational fishing competitions, although limited area, can provide us with not only willing helpers but also many more "˜research vessels"than we could ever hope to muster for a standard research project.
What we did
Every hour each boat recorded its fishing track and the location or any fish caught on a waterproof grid. Three boats were given special tasks. "˜Misty"(Mike Fifield), "˜Aquanaut"(Paul Arnold) and "˜Bluebar"(David Adams) to deploy electronic depth and temperature recorders to obtain profiles of the fishing grounds. These boats also recorded sea surface temperatures with thermometers we provided. These thermometers were to assist in our calibration of the sea surface temperature (SST) data and our temperature depth recorders.
The boats"catches were recorded at the end of each day (including tagged and released fish) and after the Sunday "˜weigh in"we were given the completed data sheets from each of the boats. We then plotted the catch by species over a 2 x 1.4 mile grid and then plotted the catch per unit effort (CPUE), which is the total catch divided by the hours spent fishing. To this was added data on sea surface temperatures and coastal landforms. This data was recorded, and beamed by satellite to Hobart, as the fishing competition was in progress.
What did we find?
A lot! Putting the science aside for one moment, the competition was a success with 314 albacore, 34 shark, 28 yellowfin tuna, 95 stripeys and a 134 kg striped marlin caught. The results were quite satisfying for us. Certainly Peter from the "˜Chicken man"was happy, he caught the record striped marlin. We don't get many of them in this neck of the woods, though at least two others were spotted over the weekend.
Back to the science: with the cooperation and assistance of the anglers we obtained catch and effort dada for over 700 square miles. Over the two days, recordings were made every hour at no less than 20 different sites that is definitely something we can't normally obtain, even with CSIRO's state of the art research vessel, the Southern Surveyor.
Unfortunately our temperature depth recorders did not work (they were experimental and we have had more success with them subsequently). The data from the thermometers was used to "˜ground truth"the SST data. As well as where fish were caught, we also obtained information on where fish were not caught.
Zero results were just as important as good catches. The plotted results show that more of the catch come from fairly close inshore where many of the competitors fished. More surprising was that the highest CPUE actually occurred offshore from the main fishing areas. But the most exciting result come when we overlaid the CPUE results on to the satellite temperature image of the area. This showed that competitors got the highest return for their efforts from cooler waters about 18 km's offshore. Reports from boat owners who worked those areas also indicated a lot of surface activity by smaller bait fish and birds.
Does this tell us anything new?
Knowledge we accumulated from the Easter weekend will be added to our database on "˜Fisheries Oceanography"which will help us better predict "˜good"fishing areas. As any good fisher knows, catch rates are higher where there is a lot of surface bait activity, where birds are working, or where you get "˜tide lines'. Colder waters are traditionally regarded as higher in nutrients, offering good fishing prospects. A look at the sea surface temperature chart shows a tongue of cold water pushing up from the south along the coastline. Further out, there is warmer water travelling south which is then mixing with this colder water and forming as eddy along the Continental Shelf. It appears, from the catch information, that waters in this general area are more productive, the eddy having a concentrating effect on bait fish, in turn attracting the top level predators which the game fishers chase.
Unfortunately it is not a simple relationship between water temperature and fish presence, let alone abundance. While most species have preferred temperature requirements they can also be found outside their preferred ranges for differing reasons such as searching for food and spawning. An example of this is seen in the Coral Sea for yellow fin and big eye tuna. Colder water species, such as big eye and southern blue fin tuna have lover preferred temperatures, around 10 to 18 degrees Celsius, while warmer water species such as yellow fin tuna and many of the marlin species prefer water in the 18 to 28 degrees Celsius.
To complicate the story even further many species, including southern blue fin, yellow fin and big eye tuna as well as broadbill swordfish and many other marlin species, exhibit daily vertical movements down to 600 m. The fish are commonly near the surface during the night and go deeper during the day. Many of the prey species that these fish feed on do the same. As it can be seen it is no easy matter trying to predict where fish are going to be, especially in relation to sea water temperature. There are many more variables which need to be incorporated and amalgamated into any work looking at predictive fisheries oceanography. It is only by gathering all the information that is available, then compiling and analysing it that we will hopefully, in the future, gain a better understanding of the fisheries oceanography relationship.
Another related project, which the CSIRO Division of Fisheries is undertaking, is the use and analysis from the SeaWiFS satellite, which instead of showing us variations in sea surface temperature, shows variations in the density of chlorophyll (primary productivity). Depending on water temperature and levels of nutrients, the oceans have varying densities of microscopic plants (phytoplankton) in them which are the vase of the marine food chain. It is these areas of higher productivity which help determine the best fishing areas. It is hoped that by analysing the data from the SeaWiFS satellite, and with the cooperation of anglers, we will be able to more accurately predict areas where the fishing is "˜good'. The CSIRO's involvement in the St Helens Easter game fishing tournament was just a trial run pilot study, to see if we could obtain quantifiable data from recreational fishers with which to expand our knowledge of fisheries oceanography. We can and thanks! Thanks go to the St Helens Game Fish Club and Chris Pratt, Barry Hardy and Sue Breen in particular for helping with this study and of course to the fisherman who took the time and effort to fill in the logs and provide data.