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MARINE RESEARCH

New GCRL Billfish Research: Atlantic Billfish Research Program

The Gulf Coast research Laboratory (GCRL) of the University of Southern Mississippi was recently awarded a research grant to conduct a study of blue marlin (Makaira nigricans) in the northern Gulf of Mexico. The grant was provided by the National Marine Fisheries Service through the agency's new Atlantic Billfish Research Program (administered by the Gulf States Marine Fisheries Commission). The GCRL research team will examine blue marlin reproductive biology, spawning habitat and nursery habitat, all of which are extremely important aspects of basic blue marlin life history. The research will be conducted during 2005 and 2006.

Although the research will focus specifically on blue marlin, the results of the study will also be useful to advance the understanding of the biology and habitat requirements of white marlin and sailfish. Project research personnel are Nancy Brown-Peterson, Jim Franks, Bruce Comyns, Eric Hoffmayer and Don Johnson (all with the Gulf Coast Research Laboratory) and Jan McDowell (with the College of William and Mary, Virginia Institute of Marine Science).

The goal of the research is to document the timing and location of blue marlin spawning and identify possible nursery areas in the north-central Gulf. This will be accomplished through investigations of adult and young (larval) specimens.

Owing to their pelagic lifestyle and highly migratory nature, only a small amount of biological data has been collected for blue marlin in the Gulf of Mexico and South Atlantic, and there is virtually no published scientific information on blue marlin biology and life history from the Gulf. Scientific information for improving management of blue marlin resources is critically lacking. This is particularly alarming in light of assessments that the Atlantic blue marlin is over-fished.

Recent collections of billfish larvae by the research team during studies of fishes that utilize Sargasssum as habitat in the north-central Gulf indicates the importance of the region as a billfish spawning area. Species-specific knowledge of the distribution and abundance of billfish larvae is important because: (1) the presence of very young larvae is the only conclusive evidence that successful adult spawning activity has occurred at, or near, the waters of their collection: and (2) larval abundance may hold promise as an indicator of the number of spawning adults that produced them.

Collections of blue marlin larvae from the north central Gulf represents a way to simultaneously obtain information on billfish spawning and nursery habitat in the region, as well as to provide information on age and growth of the species. Knowledge of the timing of female maturation and the age of larvae coupled with data on ocean currents in locations where larvae are collected, is useful to "hindcast" probable spawning locations and times. The identification of potential billfish spawning and nursery areas in the northern Gulf is critical for the protection and conservation of the species. Data from this study will provide a baseline for future assessments of the Gulf's blue marlin population for inclusion in updates of the Atlantic Billfish Management Plan.

Sargassum Study

Jim Franks, Biologist with the USM Marine Research Lab and staff view a large mat of sargassum in the Gulf of Mexico from the research vessel "R/V Tommy Munro". Divers from the vessel go under the mat taking samples and video tape different species of fish (and their abundance) that are underneath.

Under The Sargassum

Seventy Percent of the world's freshwater is contained in the Antarctic Ice Cap.

Billfish See Color

Australian researchers have examined the eyes of marlin caught over several years and have found color receptors.
The lower part of the marlin's eye, the part that looks up, contains two differently shaped cone photoreceptors that detect color. The upper part of the retina, the part that looks into deep water, does not see color.
Billfish see color when they look up to the surface.

Tuna's Magnetic Sense

In 1986 the University of Hawaii and NOAA found that yellowfin tuna sense magnetic forces on the ocean floor that may guide them in their migrations. Fishery biologists have found that tuna contain as many as 10 million magnetic crystals of the black iron mineral magnetite in their skullbones. They believe that the fish use the magnetite like a compass

Cancer in Sharks?

Studies conducted by scientists from Johns Hopkins Univ. and George Washington Univ. found cancerous tumors in sharks.
Shark cartilage may not be as effective as promoters claim.

Dolphin (mahi mahi) Grow Fast

Dr. Bob Shipp who is widely recognized as being the worlds leading expert on Gulf of Mexico fishes and is author of "Guide to Fishes of the Gulf of Mexico" stated that "An interesting fact about the common dolphin is that the fish is one of the fastest growing in the world. It's growth rate is second only to the blue marlin. A healthy bull dolphin can gain an average of 10% of their body weight per day for life. Researchers at the University of Miami are rearing common dolphin and have documented their growth rates. One dolphin grew from 1 lb to over 35 lbs in a single year, while another dolphin weighing just under 2 lbs grew to over 11 lbs in just thirty days."

Otoliths in Fish Heads Help To Age Fish

Otoliths are calcium structures located in the head of bony fishes. Otoliths are located on each side of the brain and grow in "layers" as the fish grows larger with time. Otoliths usually can be used to age fish by counting the number of "bands" that typically form on otoliths during various seasons of the year, very much like counting the rings of a tree. However, the age of some species, including a few large offshore pelagic fish, may be estimated by counting the ultra-microscopic "daily" bands that form. Fish biologists spend a great deal of time and effort processing otoliths prior to their examination under high magnification to count the age bands. Wahoo are among the most difficult offshore fish to age because their otoliths are so small (only a few mm in size) and fragile. Determining the age of fish species is an important component of determining the status of their stocks.

Yellowfin Tuna Travels 1,000 miles - Wahoo 1,707 miles

Yellowfin tuna tagged off Midway Atoll was recaptured off the Hawaiian island of Kauai eight months later by a Hawaii-based longliner. 42 pounds heavier and a foot longer than when it was tagged by the Hawaii Tuna Tagging program.

Wahoo tagged and released off Midway Island was recaptured 198 days later 1,707 miles away from midway. According to David B. Holts of the Southwest Fisheries Science Center, this represents the longest movement ever recorded for a wahoo.

Billfish have Brain Heaters	Pop-up Satellite Tags
Billfish don't need to heat their entire body to adapt to changes in water temperature. A mass of muscle attached to each eye adjusts the brain's temperature as the fish swim through varying ocean depths. "The fish have built a furnace out of muscle," says Barbara Block of the University of Chicago, who studies the seagoing space heater.	A new generation of high-tech tags has been developed. Drs. Barbara Block and Heidi Dewar of Stanford Univ. are using long release (3, 6, or 12 months) pop-up satellite tags to track movements of blue marlin in the Atlantic and Pacific oceans. The tags will record water temperature as well as the angle of inclination every two hrs. At a set time the tags release from the fish, float to the surface and 'phone home'.
Billfish Age
Rings, similar to those in trees, found in the spine of marlin help in determining its age.	Wahoo Study Continues......Click Here
Bluefin Tuna Deep Divers.....Barbara Block , Director of the Tuna Research and Conservation Center says "Bluefin dive to at least 2400 feet. Bluefin make brief descents particularly at dawn and dusk". It is believed that the tuna are following a deep scattering layer made up of squid, crustaceans and smaller organisms that travel up near the surface at night and return to the depths at daylight. Data is being obtained from tags that register the depth, ambient temperature of the water and a tuna's internal body temperature every two minutes. The current tags were designed to stop recording at 2400 feet. "The next generation of tags will record to 3,000 feet", Block says. Tags also have proven that bluefin maintain very warm body temperature even in the 40 degree range of the depths. To help their bodies generate such warmth, they spend a great deal of their time (in afternoon and evening) basking in the warm water near or at the surface.