As I approach the time when I can return to SCUBA diving, I am excited to hear tales from divers here indicating the giant sea bass (Stereolepis gigas) have once again returned to Casino Point. One of my biggest thrills is spending time observing and filming these gentle giants. Much better IMHO than sitting in a bar even if I'm drinking Great White.
Over the decades I've spent quite a bit of time with these members of the wreckfish family (Polyprionidae). They are the largest bony fish in our waters and I've dived with some that were 7 1/2 feet long and hundreds of pounds. A few years ago Dr. Larry Allen at Cal State Northridge and his team used a laser measuring device to document one that was nine feet in length. Now that is a whopper.
However, like most vertebrates, these fish begin life as a tiny fertilized egg. Once they hatch, the youngsters are quite small as well. Heck, even Dr. Bill started out as a tiny embryo and was a mere 9 lbs 4 oz at birth! Despite thousands of hours underwater, I've never been lucky enough to see the babies. Fortunately, I have dive friends like Kevin Lee who have seen and photographed them so I can experience the thrill vicariously.
My regular readers are undoubtedly aware that this fish was seriously impacted by commercial and recreational fishing. Dr. Allen states that its population numbers peaked back in 1934 and declined after that. Commercial fishers switched from hand lines to gill nets to catch them. California initiated protections on these fish beginning in the early 1980s. In 1994 the State banned gill nets within three miles of the mainland and one mile off the Channel Islands. Later the IUCN (International Union for Conservation of Nature) listed the species as critically endangered. Thanks to these protections, giant sea bass numbers have been increasing and we see them regularly in our waters during the warmer months.
Scientific understanding of their life history was lacking due to several factors. In the early years, commercially landed specimens were beheaded and gutted. This meant the otoliths in their ears which are used to age the fish were lost. In addition the overall length of these fish could not be accurately determined. This made age and size relationships impossible to determine. By eviscerating them, stomach contents could only occasionally be studied to see what they chowed down on.
Fitch and Lavenberg in 1971 published a paper indicating that young giant sea bass reached 7" at the end of their first year and twice that length at two years. Hawk and Allen (2014) have suggested they may live at least 76 years. Hopefully I'll last at least that long as well. However, estimates of their age, length and weight as they aged varied greatly in different studies.
Many of you are familiar with the use of growth rings to determine the age of trees. Hawk and Allen's recent studies looked at the growth rings in the otoliths (ear bones) to determine the age of 64 giant sea bass that were made available to them. Based on their data, growth tapered off at a length of about 6 1/2 feet. However, they were not able to separate males from females in their study since the fish's gonads were not available. Here in Catalina waters we often see smaller males with larger females, but the age of the fish is unknown.
Our giant sea bass has a closely related species, Stereolepis doederleini, in the northwest Pacific ocean but life history studies of it are also limited. The Atlantic wreckfish, Polyprion americanus, was found to reach a maximum age of about 76 years as well. Females grow larger and faster than males in another wreckfish species, the New Zealand hapuku (Polyprion oxygeneios) indicating there is sexual dimorphism.
Life history information about the giant sea bass is important in developing good fishery management plans. Incidental commercial take is one factor in mortality, but another is the impact of catch-and-release by recreational anglers. Many fishers are aware of the potential for death when they accidentally catch one and are careful in attempting to reduce this possibility.
However one study by my UCSB colleagues, Drs. Donna Schroeder and Milton Love, suggests that catch-and-release (CR) can accelerate the decline of a giant sea bass population. Beginning with 100 individuals a CR of just 1% would leave 21 fish alive after 25 years. Increasing the mortality rate to 10% would result in just six fish remaining while a CR mortality rate of 20% would cause the death of all 100 fish within 16 years! My former student and billfish expert Packy Offield found CR mortality rates of around 50% when looking at marlin.
So it is very important that the GSB produce lots of youngsters to maintain and increase population levels of these majestic fish. I know other divers like Sally Bartel have seen youngsters in Catalina waters, but I have never had that opportunity. Over on the mainland biologist Mike Couffer has been documenting them photographically. You can see his images at mikecouffer.smugmug.com. I'm hopeful that once I can get back in the water, I'll have a chance to witness them, too.
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Very early 1.25" juvenile giant sea bass and 3" later phase (courtesy of Kevin Lee); mature fish with young kelp bass for size comparison and the "business end" of an adult.
Over the decades I've spent quite a bit of time with these members of the wreckfish family (Polyprionidae). They are the largest bony fish in our waters and I've dived with some that were 7 1/2 feet long and hundreds of pounds. A few years ago Dr. Larry Allen at Cal State Northridge and his team used a laser measuring device to document one that was nine feet in length. Now that is a whopper.
However, like most vertebrates, these fish begin life as a tiny fertilized egg. Once they hatch, the youngsters are quite small as well. Heck, even Dr. Bill started out as a tiny embryo and was a mere 9 lbs 4 oz at birth! Despite thousands of hours underwater, I've never been lucky enough to see the babies. Fortunately, I have dive friends like Kevin Lee who have seen and photographed them so I can experience the thrill vicariously.
My regular readers are undoubtedly aware that this fish was seriously impacted by commercial and recreational fishing. Dr. Allen states that its population numbers peaked back in 1934 and declined after that. Commercial fishers switched from hand lines to gill nets to catch them. California initiated protections on these fish beginning in the early 1980s. In 1994 the State banned gill nets within three miles of the mainland and one mile off the Channel Islands. Later the IUCN (International Union for Conservation of Nature) listed the species as critically endangered. Thanks to these protections, giant sea bass numbers have been increasing and we see them regularly in our waters during the warmer months.
Scientific understanding of their life history was lacking due to several factors. In the early years, commercially landed specimens were beheaded and gutted. This meant the otoliths in their ears which are used to age the fish were lost. In addition the overall length of these fish could not be accurately determined. This made age and size relationships impossible to determine. By eviscerating them, stomach contents could only occasionally be studied to see what they chowed down on.
Fitch and Lavenberg in 1971 published a paper indicating that young giant sea bass reached 7" at the end of their first year and twice that length at two years. Hawk and Allen (2014) have suggested they may live at least 76 years. Hopefully I'll last at least that long as well. However, estimates of their age, length and weight as they aged varied greatly in different studies.
Many of you are familiar with the use of growth rings to determine the age of trees. Hawk and Allen's recent studies looked at the growth rings in the otoliths (ear bones) to determine the age of 64 giant sea bass that were made available to them. Based on their data, growth tapered off at a length of about 6 1/2 feet. However, they were not able to separate males from females in their study since the fish's gonads were not available. Here in Catalina waters we often see smaller males with larger females, but the age of the fish is unknown.
Our giant sea bass has a closely related species, Stereolepis doederleini, in the northwest Pacific ocean but life history studies of it are also limited. The Atlantic wreckfish, Polyprion americanus, was found to reach a maximum age of about 76 years as well. Females grow larger and faster than males in another wreckfish species, the New Zealand hapuku (Polyprion oxygeneios) indicating there is sexual dimorphism.
Life history information about the giant sea bass is important in developing good fishery management plans. Incidental commercial take is one factor in mortality, but another is the impact of catch-and-release by recreational anglers. Many fishers are aware of the potential for death when they accidentally catch one and are careful in attempting to reduce this possibility.
However one study by my UCSB colleagues, Drs. Donna Schroeder and Milton Love, suggests that catch-and-release (CR) can accelerate the decline of a giant sea bass population. Beginning with 100 individuals a CR of just 1% would leave 21 fish alive after 25 years. Increasing the mortality rate to 10% would result in just six fish remaining while a CR mortality rate of 20% would cause the death of all 100 fish within 16 years! My former student and billfish expert Packy Offield found CR mortality rates of around 50% when looking at marlin.
So it is very important that the GSB produce lots of youngsters to maintain and increase population levels of these majestic fish. I know other divers like Sally Bartel have seen youngsters in Catalina waters, but I have never had that opportunity. Over on the mainland biologist Mike Couffer has been documenting them photographically. You can see his images at mikecouffer.smugmug.com. I'm hopeful that once I can get back in the water, I'll have a chance to witness them, too.
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Very early 1.25" juvenile giant sea bass and 3" later phase (courtesy of Kevin Lee); mature fish with young kelp bass for size comparison and the "business end" of an adult.
