Lahaina Harbor boats enjoy great early summertime blue marlin bite
As one might suspect of highly mobile creatures like blue marlin, the picture of their population in any one fishing ground is not static.
The dynamic nature of the blue marlin’s lifestyle is reflected by seasonal changes in the number of fish caught, as well as by changes in the size composition and sex ratio of the population.
The large summer catches are dominated by males, and these smaller animals outnumber the larger females by from two to six times. Late fall catches show more equal numbers of males and females, and small spring catches show the larger females two to seven times more numerous than males.
Evidence from several different kinds of fisheries, including sport fishing and long-lining, indicates that the unequal representation of the sexes on the grounds does not appear to be due to differences in feeding habits of the sexes or to the kinds of fishing gear used.
Then why the change? There is a very strong relationship between the sex ratio and the reproductive condition of the fish. Samples with the highest male to female ratios contained the highest percentage of reproductive individuals.
Where the sex ratio was nearly equal (fall) or females outnumbered males (spring), few of the fish showed signs of reproductive activity.
Similar changes in catch, sex ratio and size composition by season have been observed in both Pacific and Atlantic populations of blue marlin, as well as in striped and black marlin. In these studies, the large influx of males corresponded to the beginning of the fishing season.
Females in smaller numbers dominated the offseason fishing grounds during the non-reproductive season. Some researchers have recommended using the sex ratio change as an indication of the timing of the reproductive season.
But why should there be so many males present during the reproductive season? In Hawaii and elsewhere, anglers and boat captains report that during the summer months, they frequently see a single large marlin (presumably female) escorted by several smaller fish (presumably males).
Perhaps the presence of several males is needed to ensure high fertilization success of the female’s millions of eggs. In Hawaii, the summer sex ratio reflects the influx of large numbers of males, perhaps to a “spawning ground” close to the islands to which large females are attracted when ready to spawn.
Some longtime Hawaiian fishermen even suggest that there are distinct areas where marlin are frequently seen engaged in possible spawning behavior.
The end of the May spring bite saw 20 blue marlin weighed and another nine released, totaling 29 fish. Of the 20 blue marlin weighed, I classified 13 of them. There were six small males between 85.8 and 181.5 pounds. One blue weighing 85.6 pounds was female.
There were another six blue marlin weighed (377.7, 388.7, 444.4, 487.5, 503.8 and 1,058.3 pounds). With 99 percent of all blue marlin over 300 pounds being female, I presumed that these fish were all female.
Of the nine blue marlin that were released, they were 75-275 pounds. Seven of them were between 75 and 150 pounds, presuming that these fish were male.
The beginning summertime blue marlin bite during June saw the best month for total blue marlin since 2011, with 23 making the scales (most blues weighed since July 2013) and another 16 released (most blues released since August 2011), totaling 39 fish (highest total blues since August 2011).
Of the 23 blue marlin that were weighed, I sexed 18 of them. There were 16 small males between 106.3 and 195.8 pounds, with two females weighing 198.0 and 272.4 pounds, which was the largest blue weighed during the month.
Of the 16 blue marlin released during June between 80 and 400 pounds, 11 were between 80 and 175 pounds. I would presume that 99 percent of these fish were male and 99 percent of the five released between 200 and 400 pounds were female.
July raised the numbers for the best month for blue marlin since 2011, with 27 being weighed (most blues weighed since August 2011) and another 32 released (most blues released since November 1995), totaling 59 fish (highest total blues since July 2011).
Of the 27 blue marlin that were weighed, I sexed 24 of them. There were 18 small males between 94.0 and 220.2 pounds, with seven females between 121.2 and 578.6 pounds. There were four blue marlin over 400 pounds (412.5, 553.3, 568.7, 578.6) that were female.
Of the 32 blue marlin released during July between 100 to 350 pounds, 25 were between 100 and 180 pounds. I would also presume that 99 percent of these fish were male. The seven blues released between 200 and 350 pounds presumably were 99 percent female.