What do we really know about marlins? How big do they get? How fast do they swim? Do they see colours? Do they change sex as they grow? These questions are amongst the common ones asked by anglers and onlookers at tournament "weigh-ins" after they have asked what it is. Since the world leading policy by Australian fisheries to exclude commercial marlin fishing from prime recreational waters since 1987 the east coast has seen the development of what could be argued the worlds best recreational bill fishery. But have we learned much about marlin since then? It is the aim of these articles is to answer some of the questions posed above and to provide a review of the state of our knowledge. First however, a bit of background about marlin in the Pacific Ocean is in order.

The tropical and subtropical waters of the Pacific Ocean are home to three of the largest and fastest blue water predators, the black, blue and striped marlins. Blue marlin have been weighed in at over 800 kg (1800 lbs) and have been estimated in excess of 900 kg from carcasses from commercial longline fishing vessels. Their size, speed and athletic ability make marlin spectacular sporting fishes, sought after by recreational fishermen and women who often target marlins and their billfish relatives in special billfish tournaments. Marlin are also highly regarded at the table and support significant commercial billfish fisheries.

The total Pacific Ocean catch of marlins is estimated to have been around 30,000 tonnes in 1985, about 250,000 fish. Of this, about 90% is taken by longline fishing vessels which primarily target tuna species. Billfish comprise about 18% of the total tuna longline catch and represent an important by catch for these vessels. The recreational and subsistence billfish catches are believed to be small but not insignificant compared with the longline by catch. The rapid growth and subsequent decline of the recreational and commercial swordfish fisheries off the east coast of Florida between 1977 and 1985 has helped to focus attention on billfish species and great progress has recently been made toward billfish management. The International Commission for the Conservation of Atlantic Tunas (ICCAT) has been able to negotiate agreements on management strategies for the Atlantic Ocean and action management plans such as the Atlantic Billfish Management Plan (Approved by US Secretary of Commerce in 1988) which seeks to "Maintain the highest availability of billfishes for the recreational fishery...". The Governments of Australia since 1979, Mexico since 1983, and New Zealand since 1987 have attempted to enhance their recreational billfish fisheries by exclusion of longline vessels from parts of their 200 mile Exclusive Economic Zones (EEZ).

These actions have highlighted many features of recreational billfish fisheries including their environmental sensitivity, high financial return per fish captured and significant contributions to the successful cooperative tag and release programmes.

The need to bring together all available information on billfishes from time to time has been recognised and acted upon by several organisations. The National Marine Fisheries Service (NMFS) sponsored the first International Billfish Symposium in 1972 and co-sponsored with the National Coalition for Marine Conservation (NCMC) and a number of other bodies the second International Billfish Symposium in 1988. Justifiably these meetings were mostly concerned with the problems surrounding effective management and considered at length subjects such as stock identification and assessment, age, growth and early life history development and reproduction. However, as a result there is almost nothing about the structure or function contained within the proceedings of these symposia.

These articles will concentrate on how these magnificent fishes live their daily lives. How they swim, breathe, see, eat and reproduce rather than on aspects of the fisheries for marlins. Much of the information for the articles is drawn from my book, PACIFIC MARLINS: ANATOMY AND PHYSIOLOGY available from the author directly.

All of the billfishes are bony fishes (members of the subclass Teleostei) of the order Perciformes, suborder Xiphioid. They belong to either the family Xiphiidae which has but one species, the broadbill swordfish (Xiphias Gladius) or the family Istiophoridae.

The family Istiophoridae is comprised of three genera:

• Istiophorus, the sailfishes,
• Tetrapturus, the spearfishes and striped and white marlin, and
• Makaira, the blue and black marlins.

Billfishes are found in the tropical and temperate waters of the oceans mentioned. The following list is not in phylogenetic order.

*According to Nakamura (1983), there are two species of blue marlin. This is not widely accepted, and Davie treats all information on blue marlin as pertaining to one species, Makaira nigricans.

For completeness however, Nakamura's two blue marlin species are presented:

Diagnostic features for separating Pacific marlin species, striped, blue and black marlin, are briefly described below:

Striped marlin: Height of first dorsal fin as high as, or higher than maximum body depth; blue and black marlin first dorsal fin height less than maximum body depth. Twelve precaudal and 12 caudal vertebrae: blue and black marlin have 11 precaudal and 13 caudal vertebrae. Body laterally compressed: blue and black marlin have rounded bodies.

Blue marlin: Pectoral fin may be retracted (adducted) against body; black marlin have rigid pectoral fins. Looped (Indo-Pacific) or hexagonal (Atlantic) lateral line pattern; black and striped marlin have simple (single) lateral line.

Black marlin: Pectoral fin non-adductable. Insertion of second dorsal fin is cranial of the insertion of the second anal fin; blue and striped marlin second dorsal fin more caudal than second anal fin.

Peter Davie is a senior lecturer in Physiology and Anatomy, Massey University, Palmerston North, New Zealand. His research interests are in the areas of cardiovascular and respiratory anatomy and physiology of fishes as diverse as hagfish and marlins. He studied at Canterbury University for his BSc (Hons) and Ph.D. He was a Killam Postdoctoral Fellow at the University of British Columbia in 1979 and 1980 after which he took up his present position at Massey University. He has been associated with the New Zealand Big Game Fishing Council since 1983 and has been active in promoting gamefish conservation in New Zealand. An Affiliated Scientist with the Pacific Gamefish research Foundation, Hawaii since 1985 he has worked at their laboratory in Kailua-Kona, Hawaii several times for periods up to four months.