The numbers of larvae larger than 7.75 mm. taken by plankton nets are undoubtedly affected by "net dodging." Most other larval fish taken with jack mackerel in plankton nets show an increase in the ratio of night-caught to daycaught larvae with increasing size of larvae. Farris found that the ratio of night-caught to day-caught larval jack mackerel remained approximately 1:1 for larvae 2 to 12 mm. He concluded that jack mackerel do not evade the net. A second interpretation is that they avoid the net equally well both by day and night.

The principal rays of the dorsal fin first appear at 5 to 6 mm, and a full complement is attained by 8 mm. The remaining fins begin to form at 6 to 8 mm. The resulting increased motility could decrease the capture of larvae by the net from a probable 100 percent (over the length range 3.50 to 7.75 mm) of the larvae available to the net to considerably less.

Survival also appears to increase at this point. If the initial survival rate continued to 18.5 mm,, only 1 larva of the original 1 million would survive and the adult stock could not replace itself. The first reduction in mortality appears to take place at about 8 mm. when the larvae become motile.

The apparent relation between numbers of larvae and length for the range 8.75 to 13.75 mm. may be described by log Y = 5.57267 0.24594X, at this size range survival is 57 percent for each millimeter of length increase. This rate of survival would reduce the larval population to 1 fish at 22.5 mm. More probably, the larval mortality is decreasing with increasing size and motility of the fish above 8 mm; the increasing motility of the fish also increases its ability to avoid the net, thus causing progressively greater under sampling of fish over 8 mm. There is no indication of a "critical period" in survival, and the only "abrupt" change in the survival curve occurs at the time of fin formation.

3.23 Adolescent phase

Little is known about the juvenile jack mackerel. Food studies show that copepods, euphausiids and pteropods constitute most of the food in stomachs, and that copepods are a more important food among juveniles than among adults (Anonymous, 1953).

3.3 Adult phase

3.31 Longevity

Most of the fish taken in the commercial catch are less than 6 years old; the majority are 2, 3, and 4 years old. On rare occasions very large jack mackerel from 10 to over 25

One study of food habits revealed that 90 percent by numbers of identifiable items in jack mackerel stomachs consisted of euphausiids, large copepods, and pteropods. Samples from cannery landings showed that at times jack mackerel feed almost exclusively on juvenile squid and anchovies. Large jack mackerel taken in offshore waters at night contained lantern fish. Both the mackerel and lantern fish were probably attracted to a light suspended over the stern of the vessel. Large jack mackerel taken by the sport fishery are usually caught with large adult anchovies as bait (Fitch, 1956).

Jack mackerel have been taken incidentally to the sardine and Pacific mackerel fisheries for many years by the same gear used in these fisheries. When the mackerel fishery developed suddenly in 1947 because of the decline in sardines and to a lesser extent Pacific mackerel, the purse seines of the sardine and Pacific mackerel fishery continued to be used for the jack mackerel. Scofield (1951) described in detail purse seines and other round haul nets that have been used in California fisheries. Before the development of the fishery for jack mackerel they were also taken in small quantities in the ring nets and lampara nets used by the sardine fishery before the purse seine came into general use.

Jack mackerel are also taken by the fishermen who fish for Pacific mackerel for the fresh fish market and to a lesser extent for canneries. Various methods have been and are used in this fishery, including hand lines, long lines, jigs, gill nets, and scoop nets, often in conjunction with chumming and/or lights (Croker, 1933, 1938).

Improvements in ship gear and fishing methods of the purse seine fleet include installation of ship-to-ship radios, echo-sounding gear, and power blocks, and the use of motor skiffs, synthetic netting materials, and airplane scouting.

5.12 Boats

The jack mackerel is taken primarily as a substitute or alternate cannery fish by the sardine fishing fleet. The sardine fleet consists of large purse seiners (over 60 feet or 18.3 meters in length) and assorted smaller purse seiners and lampara boats that are used in other fisheries when sardines are not available. Since the big increase in jack mackerel landings in 1947, this fleet attained its largest size during the 1949-50 season when it consisted of 372 vessels (including 135 smaller boats). In the 1960-61 season the California sardine fleet consisted of only 28 vessels (11 large purse seiners, 2 small purse seiners, and 15 lampara boats).

5.2 Fishing areas

Most jack mackerel are landed in the Los Angeles area (Roedel, 1953). Because this fishery is so closely allied to the sardine fishery, the area of the jack mackerel fishery closely coincides with that of the sardine (Fig. 6). The purse seiners are primarily

seeking sardines; if sardines are scarce and there is a market for jack mackerel, these fish are taken instead whenever encountered. Actually the jack mackerel is distributed farther offshore than the sardine. In the 1952-53 sardine season the sardine catch was only about 3,000 tons, compared to over 120,000 tons the previous year. In the same season the jack mackerel catch was a record 73,000 tons, but 67 percent of this catch was made in the Tanner Bank-Cortez Bank area about 80 nautical miles offshore (Clothier and Greenhood, 1956). When sardines are more abundant the purse seiners do not range so far offshore.

based on facilities available for handling the fish and on economic considerations.

6.12 Protection of portions of population

California has regulations pertaining to fishing gear and craft and also restrictions on commercial fishing in several relatively small areas. These regulations were not passed specifically to control the jack mackerel fishery and probably have little or no effect on it. There are no closed seasons or other restrictions on the jack mackerel fishery. California law prohibits the use of fish for reduction except that the fish offal may be reduced. The law also provides that the Fish and Game Commission may grant permits for the reduction of whole fish, but none have been granted for any species except sardines, and even reduction of sardines has not been allowed since 1948.