Post by Reticulatus on Feb 26, 2012 0:48:55 GMT -5
Giant Sea Bass-Stereolepis gigas
Giant sea bass are a robust fish, starting out life as a brightly colored orange juvenile with large black spots.
As the fish grows it loses the orange coloration and takes on a bronzy purple hue. The spots slowly fade as the fish gets larger and darker, with large adults appearing solid black to gray with a white underside. As with its close relatives, the groupers, giant sea bass are capable of rapid and dramatic color changes. Large fish retain the ability to display large black spots, and can take on a bicolor appearance (light below, dark above), assume white mottling, or simply change from jet black to light gray. It is assumed that these color changes are a form of communication between individuals and/or an indication of stress. As implied by the name, the single most dramatic feature of giant sea bass is their large size. The International Game Fish Association all-tackle world record for this species is 563 pounds 8 ounces, caught at Anacapa Island in 1968. Giant sea bass reach lengths in excess of seven feet, and are nearly as big around as they are long.
Geographic and Depth Distribution: Essential Habitat
Despite the conspicuous size and protected status of giant sea bass, there are no published scientific studies to provide us with details of the biology and habits of this creature. The late John E. Fitch amassed an important historical data set while he worked for the California Department of Fish and Game. He kept records from catches landed in California from both commercial and recreational fishermen that were fishing in Mexico and California. Fitch’s notes provide some insight into the magnitude of the fishery, size of individual fish and locations that were targeted for giant sea bass. Through numerous examinations of individual fish Fitch was able to estimate the spawning season and attempt to decipher how old these fish can get. Recent research by this author has been able to validate some of Fitch’s findings, but in other cases correct some popular mistakes.
In the eastern Pacific giant sea bass range from Humboldt Bay to the tip of Baja California, and occur in the northern half of the Gulf of California. Some authors have stated this species is also found along the coast of northern Japan and the Sea of Japan, but this appears to be a case of mistaken identity. Within California this species is rarely found north of Point Conception. Adult giant sea bass seem to prefer the edges of nearshore rocky reefs. These reefs are relatively shallow (10-40 m) and often support thriving kelp beds. Although the kelp may disappear due to a strong El Nino or overgrazing by sea urchins, giant sea bass will remain at the reef even in the absence of kelp. At certain times of the year adults can be found well away from the reef, foraging over sandy bottom for spawning squid.
The habitat preferences of the orange juvenile phase remain a mystery. Young fish remain orange with black spots at least until they are 20 cm long. Milton Love from the University of California, Santa Cruz, reports finding this stage among drifting kelp scattered over the bottom in 6-10 m of water. I have captured a number of these juveniles over the soft muddy bottom outside of the Long Beach Breakwater, and over flat sandy bottom in Santa Monica Bay. Larger juveniles are sometimes caught over deep ridges (70-80 m) off the coast of Del Mar by anglers targeting rockfish. I have also found juveniles up to 14 kg over flat sandy bottom, as well as the same areas usually associated with adults. Clearly much more work needs to be done before we can accurately describe the early life history stages of this species.
Age and Growth
Unfortunately a comprehensive study of age and growth was never conducted when the species was plentiful in California and Mexico. A study of this type requires examination of a very large number of individuals; given the depressed population and protected status it is unlikely an aging study of giant sea bass will be completed in the near future. Ages for giant sea bass have been frequently mentioned in the popular literature, apparently extracted from Fitch’s notes. Fitch did assign ages to some specimens, but it must be noted that this was based on counting the number of rings found on individual scales. Aging fish in this manner has proven to work for many freshwater fishes, but it is notoriously unreliable for marine species. A small bone in the inner ear, called an otolith, is the standard structure used for aging marine fishes. This bone is usually sectioned and examined under a microscope for rings that are then counted, similar to the rings in a tree.
I have examined otoliths and scales from individual giant sea bass, and concluded that otoliths are probably a reliable structure for aging this species, but scales are not. For example, five fish of the same size will be assigned widely varying ages when using scales, but very similar ages when using otoliths. Because of this, previously published aging data based on Fitch’s notes must be disregarded. I have aged only 40 individuals, all less than 200 pounds. Such a small data set does not allow for much interpretation, but it is safe to say these fish grow slowly and likely live a very long time. Our oldest specimen was 20 years old, and this fish was less than a third of the maximum recorded size for this species. Some estimates from our data are: 6 years to reach 30 pounds, 10 years to reach 100 pounds and 15 years to reach 150 pounds. Rate of ring deposition in giant sea bass otoliths has not been validated, and many more specimens are required before a more thorough analysis can be completed.
Spawning has never been observed in the field, but by examining the gonads of a large number of giant sea bass, Fitch was able to determine that spawning occurs between July and September. A proper size of maturity study has not been conducted, but I have found males to be mature as small as 18 kg, and Fitch noted females maturing at 23-27 kg. Anecdotal information suggests that giant sea bass aggregate at specific locations and times to spawn. Landings data from party boats fishing in Mexico strongly indicate that these spawning aggregations do occur. Because of the large size of this species, females are capable of producing enormous numbers of eggs. The ovaries of a 145 kg specimen contained an estimated 60 million eggs. Fertile, hydrated giant sea bass eggs are relatively large for a marine species, measuring about 1.6 mm in diameter. The eggs float to the surface and hatch in about 24-36 hours. The larvae drift and feed in the plankton for about a month before settling to the bottom and beginning their lives as juveniles. Giant sea bass have spawned in captivity several times; most recently at the Long Beach Aquarium of the Pacific. A single pair of giant sea bass have spawned in two successive years at the aquarium, spawning nearly weekly beginning in June and ending in August or September. Since these fish are held in an aquarium with artificial lighting and constant water temperature (18.3 C), these observations cannot be used to verify the timing and frequency of natural spawning. On one occasion researchers at the Hubbs-Seaworld Research Institute successfully hatched and reared giant sea bass larvae through settlement. Subsequent attempts to raise them in captivity have failed.
Food
The feeding habits of giant sea bass have been misrepresented in the past, most likely due to incorrect interpretation of Fitch’s early observations. Of the hundreds of fish examined by Fitch, one was noted to have bonito in its stomach.
This has caused subsequent authors to claim this as an important prey species, in fact one book states giant sea bass routinely run down bonito. From my own personal observations of this species in the lab and in the field I can safely say that this simply is not true. Upon examination of fish caught in Mexico I found the most important prey items to be sting rays, skates, lobster, crabs, various flatfish, small sharks, mantis shrimp and an occasional kelp bass or barred sand bass. Fitch looked at 50 stomachs and his notes add blacksmith, ocean whitefish, red crab, sargo, sheephead, octopus and squid to the list. Giant sea bass are not built for sustained speed, and the vast majority of their prey are organisms that live on the bottom. These organisms, located crawling across the substrate or buried just below the surface, are drawn into the mouth of a giant sea bass by the vacuum produced when the huge mouth is rapidly opened. Certainly some midwater fish are ambushed and sucked in by giant sea bass lurking in the shadows of the kelp, but it is very likely that the 9 bonito reportedly found by Fitch in the stomach of one 196 kg specimen was the bait and/or chum used by the fisherman to catch his prize.
Giant sea bass themselves are likely eaten by a variety of fishes and marine mammals when they are small. But as they grow only man and large sharks have the ability to eat them.
Toxins in the Environment
Giant sea bass live in close association with the bottom throughout all but the short period of time they spend as planktonic larvae. The things they eat live in and on the substrate, and giant sea bass themselves frequently rest on the bottom. This way of life has resulted in what may be a very serious problem for this species. Unfortunately the sediments along the coast of southern California carry very high loads of toxins. In fact, an area off the Palos Verdes peninsula is thought to contain higher levels of DDE (a breakdown product of DDT) than anywhere else in the world oceans. PCB is another pollutant that is prevalent along the coast of southern California. Many forms of invertebrates live in these sediments, ingesting the pollutants along with the organic material they feed on to survive. Although these organisms occupy very low trophic levels, they can not metabolize or excrete the toxins; instead, they are passed up the food chain in increasing concentrations. Long lived animals and top level predators accumulate the highest levels of toxins. I have tested tissues from several giant sea bass caught in southern California and found them to be carrying extremely high body burdens of DDE and PCB. I ran the same test on fish collected 200 miles south of the Mexican border, and found these fish to be free of toxins. It seems that California populations of giant sea bass, a very long lived mid-level predator, may be suffering from more than just overfishing. DDE and PCB have been found to affect reproduction in other species of fish, as well as amphibians, reptiles and birds. These compounds are concentrated in fatty tissues, like the brain, liver and gonads. Mature eggs carry some of the highest concentrations, levels that may be found to interfere with normal development of the larvae. Since DDE has been found to be an estrogen mimic, it may also cause males to change into females, or interfere with normal reproductive behavior. This is an area that is in need of much more research before we will know how serious a threat these toxins are to the recovery of the giant sea bass population in California.
Behavior and Migrations
It is presumed that giant sea bass migrate to specific sites to spawn. This was almost certainly the case prior to the exploitation of the spawning aggregations, but it is not known how far individuals traveled to participate in the aggregation, or whether these migrations take place today. The process of site selection for spawning aggregations is not well understood, but experimental manipulation of small aggregating reef species suggest that once a site is selected young fish learn its location from older fish. In this way, the same traditional spawning aggregation sites are used by subsequent generations of fish. Once the learning cycle has been broken it is not known how a new (or the same) spawning aggregation may or may not form. The population may have to reach a particular density before the process of forming annual spawning aggregations becomes a possibility. These questions have yet to be answered. Through my studies I have found that giant sea bass are found in groups year round at a few locations in southern California. Although anglers that come across one of these areas and hook several giant sea bass in one day may be led to believe that this species is thriving, giant sea bass remain absent from the vast majority of our coast. It is likely that these fish are gregarious, and after heavy exploitation the population has collapsed to a very few focal points where they can be found in healthy numbers.
Giant sea bass are a robust fish, starting out life as a brightly colored orange juvenile with large black spots.
As the fish grows it loses the orange coloration and takes on a bronzy purple hue. The spots slowly fade as the fish gets larger and darker, with large adults appearing solid black to gray with a white underside. As with its close relatives, the groupers, giant sea bass are capable of rapid and dramatic color changes. Large fish retain the ability to display large black spots, and can take on a bicolor appearance (light below, dark above), assume white mottling, or simply change from jet black to light gray. It is assumed that these color changes are a form of communication between individuals and/or an indication of stress. As implied by the name, the single most dramatic feature of giant sea bass is their large size. The International Game Fish Association all-tackle world record for this species is 563 pounds 8 ounces, caught at Anacapa Island in 1968. Giant sea bass reach lengths in excess of seven feet, and are nearly as big around as they are long.
Geographic and Depth Distribution: Essential Habitat
Despite the conspicuous size and protected status of giant sea bass, there are no published scientific studies to provide us with details of the biology and habits of this creature. The late John E. Fitch amassed an important historical data set while he worked for the California Department of Fish and Game. He kept records from catches landed in California from both commercial and recreational fishermen that were fishing in Mexico and California. Fitch’s notes provide some insight into the magnitude of the fishery, size of individual fish and locations that were targeted for giant sea bass. Through numerous examinations of individual fish Fitch was able to estimate the spawning season and attempt to decipher how old these fish can get. Recent research by this author has been able to validate some of Fitch’s findings, but in other cases correct some popular mistakes.
In the eastern Pacific giant sea bass range from Humboldt Bay to the tip of Baja California, and occur in the northern half of the Gulf of California. Some authors have stated this species is also found along the coast of northern Japan and the Sea of Japan, but this appears to be a case of mistaken identity. Within California this species is rarely found north of Point Conception. Adult giant sea bass seem to prefer the edges of nearshore rocky reefs. These reefs are relatively shallow (10-40 m) and often support thriving kelp beds. Although the kelp may disappear due to a strong El Nino or overgrazing by sea urchins, giant sea bass will remain at the reef even in the absence of kelp. At certain times of the year adults can be found well away from the reef, foraging over sandy bottom for spawning squid.
The habitat preferences of the orange juvenile phase remain a mystery. Young fish remain orange with black spots at least until they are 20 cm long. Milton Love from the University of California, Santa Cruz, reports finding this stage among drifting kelp scattered over the bottom in 6-10 m of water. I have captured a number of these juveniles over the soft muddy bottom outside of the Long Beach Breakwater, and over flat sandy bottom in Santa Monica Bay. Larger juveniles are sometimes caught over deep ridges (70-80 m) off the coast of Del Mar by anglers targeting rockfish. I have also found juveniles up to 14 kg over flat sandy bottom, as well as the same areas usually associated with adults. Clearly much more work needs to be done before we can accurately describe the early life history stages of this species.
Age and Growth
Unfortunately a comprehensive study of age and growth was never conducted when the species was plentiful in California and Mexico. A study of this type requires examination of a very large number of individuals; given the depressed population and protected status it is unlikely an aging study of giant sea bass will be completed in the near future. Ages for giant sea bass have been frequently mentioned in the popular literature, apparently extracted from Fitch’s notes. Fitch did assign ages to some specimens, but it must be noted that this was based on counting the number of rings found on individual scales. Aging fish in this manner has proven to work for many freshwater fishes, but it is notoriously unreliable for marine species. A small bone in the inner ear, called an otolith, is the standard structure used for aging marine fishes. This bone is usually sectioned and examined under a microscope for rings that are then counted, similar to the rings in a tree.
I have examined otoliths and scales from individual giant sea bass, and concluded that otoliths are probably a reliable structure for aging this species, but scales are not. For example, five fish of the same size will be assigned widely varying ages when using scales, but very similar ages when using otoliths. Because of this, previously published aging data based on Fitch’s notes must be disregarded. I have aged only 40 individuals, all less than 200 pounds. Such a small data set does not allow for much interpretation, but it is safe to say these fish grow slowly and likely live a very long time. Our oldest specimen was 20 years old, and this fish was less than a third of the maximum recorded size for this species. Some estimates from our data are: 6 years to reach 30 pounds, 10 years to reach 100 pounds and 15 years to reach 150 pounds. Rate of ring deposition in giant sea bass otoliths has not been validated, and many more specimens are required before a more thorough analysis can be completed.
Spawning has never been observed in the field, but by examining the gonads of a large number of giant sea bass, Fitch was able to determine that spawning occurs between July and September. A proper size of maturity study has not been conducted, but I have found males to be mature as small as 18 kg, and Fitch noted females maturing at 23-27 kg. Anecdotal information suggests that giant sea bass aggregate at specific locations and times to spawn. Landings data from party boats fishing in Mexico strongly indicate that these spawning aggregations do occur. Because of the large size of this species, females are capable of producing enormous numbers of eggs. The ovaries of a 145 kg specimen contained an estimated 60 million eggs. Fertile, hydrated giant sea bass eggs are relatively large for a marine species, measuring about 1.6 mm in diameter. The eggs float to the surface and hatch in about 24-36 hours. The larvae drift and feed in the plankton for about a month before settling to the bottom and beginning their lives as juveniles. Giant sea bass have spawned in captivity several times; most recently at the Long Beach Aquarium of the Pacific. A single pair of giant sea bass have spawned in two successive years at the aquarium, spawning nearly weekly beginning in June and ending in August or September. Since these fish are held in an aquarium with artificial lighting and constant water temperature (18.3 C), these observations cannot be used to verify the timing and frequency of natural spawning. On one occasion researchers at the Hubbs-Seaworld Research Institute successfully hatched and reared giant sea bass larvae through settlement. Subsequent attempts to raise them in captivity have failed.
Food
The feeding habits of giant sea bass have been misrepresented in the past, most likely due to incorrect interpretation of Fitch’s early observations. Of the hundreds of fish examined by Fitch, one was noted to have bonito in its stomach.
This has caused subsequent authors to claim this as an important prey species, in fact one book states giant sea bass routinely run down bonito. From my own personal observations of this species in the lab and in the field I can safely say that this simply is not true. Upon examination of fish caught in Mexico I found the most important prey items to be sting rays, skates, lobster, crabs, various flatfish, small sharks, mantis shrimp and an occasional kelp bass or barred sand bass. Fitch looked at 50 stomachs and his notes add blacksmith, ocean whitefish, red crab, sargo, sheephead, octopus and squid to the list. Giant sea bass are not built for sustained speed, and the vast majority of their prey are organisms that live on the bottom. These organisms, located crawling across the substrate or buried just below the surface, are drawn into the mouth of a giant sea bass by the vacuum produced when the huge mouth is rapidly opened. Certainly some midwater fish are ambushed and sucked in by giant sea bass lurking in the shadows of the kelp, but it is very likely that the 9 bonito reportedly found by Fitch in the stomach of one 196 kg specimen was the bait and/or chum used by the fisherman to catch his prize.
Giant sea bass themselves are likely eaten by a variety of fishes and marine mammals when they are small. But as they grow only man and large sharks have the ability to eat them.
Toxins in the Environment
Giant sea bass live in close association with the bottom throughout all but the short period of time they spend as planktonic larvae. The things they eat live in and on the substrate, and giant sea bass themselves frequently rest on the bottom. This way of life has resulted in what may be a very serious problem for this species. Unfortunately the sediments along the coast of southern California carry very high loads of toxins. In fact, an area off the Palos Verdes peninsula is thought to contain higher levels of DDE (a breakdown product of DDT) than anywhere else in the world oceans. PCB is another pollutant that is prevalent along the coast of southern California. Many forms of invertebrates live in these sediments, ingesting the pollutants along with the organic material they feed on to survive. Although these organisms occupy very low trophic levels, they can not metabolize or excrete the toxins; instead, they are passed up the food chain in increasing concentrations. Long lived animals and top level predators accumulate the highest levels of toxins. I have tested tissues from several giant sea bass caught in southern California and found them to be carrying extremely high body burdens of DDE and PCB. I ran the same test on fish collected 200 miles south of the Mexican border, and found these fish to be free of toxins. It seems that California populations of giant sea bass, a very long lived mid-level predator, may be suffering from more than just overfishing. DDE and PCB have been found to affect reproduction in other species of fish, as well as amphibians, reptiles and birds. These compounds are concentrated in fatty tissues, like the brain, liver and gonads. Mature eggs carry some of the highest concentrations, levels that may be found to interfere with normal development of the larvae. Since DDE has been found to be an estrogen mimic, it may also cause males to change into females, or interfere with normal reproductive behavior. This is an area that is in need of much more research before we will know how serious a threat these toxins are to the recovery of the giant sea bass population in California.
Behavior and Migrations
It is presumed that giant sea bass migrate to specific sites to spawn. This was almost certainly the case prior to the exploitation of the spawning aggregations, but it is not known how far individuals traveled to participate in the aggregation, or whether these migrations take place today. The process of site selection for spawning aggregations is not well understood, but experimental manipulation of small aggregating reef species suggest that once a site is selected young fish learn its location from older fish. In this way, the same traditional spawning aggregation sites are used by subsequent generations of fish. Once the learning cycle has been broken it is not known how a new (or the same) spawning aggregation may or may not form. The population may have to reach a particular density before the process of forming annual spawning aggregations becomes a possibility. These questions have yet to be answered. Through my studies I have found that giant sea bass are found in groups year round at a few locations in southern California. Although anglers that come across one of these areas and hook several giant sea bass in one day may be led to believe that this species is thriving, giant sea bass remain absent from the vast majority of our coast. It is likely that these fish are gregarious, and after heavy exploitation the population has collapsed to a very few focal points where they can be found in healthy numbers.
