Herring: Expectations for a New Millennium 455 Alaska Sea Grant College Program • AK-SG-01-04, 2001 Survival of Pacific Herring Eggs on Giant Kelp in San Francisco Bay Sara Peterson San Francisco State University, Department of Biology –Larson Lab, San Francisco, California Extended Abstract An eggs-on-kelp fishery for Pacific herring (Clupea pallasii ) roe operates in San Francisco Bay during the winter spawning period. During the past 10 years, eggs-on-kelp harvesting has developed into a substantial eco- nomic portion of the commercial herring roe fishery. Management of this fishing method is relatively new, and there are several biological ques- tions about the effect of this fishery on the herring population. Giant kelp (Macrocystis sp.) is harvested from Monterey or southern California and suspended from open rafts immediately prior to the beginning of a spawn. If kelp is suspended too early, or the size of the spawning school is too small, the eggs-on-kelp product may be inadequate for market. In either of these cases, eggs-on-kelp is discarded with the assumption that the herring eggs will continue to develop and hatch. Macrocystis is not native to San Francisco Bay, and deteriorates at low salinities (Lobban et al.1985). The viability of kelp as a substrate for herring egg development is unknown. From a fishery management standpoint, the question of egg survival on discarded kelp is one of the unknown factors in deciding whether the amount of kelp used in the fishery should be regulated. The purpose of this study was to determine how the condition of unharvested and dis- carded kelp, along with other factors, affects the survival and hatching of herring eggs. This study took place from January to March 1999, in Sausalito and San Francisco, California. I suspended kelp, obtained from fishery partici- pants, on several small (1 m2) rafts. In order to observe kelp at different stages of deterioration, the kelp was suspended both several days (2-5) prior to a spawning event and as soon as possible to the first day of spawn- ing. Temperature and salinity were recorded on each sampling day. Once a spawning event ceased (fish were no longer observed in the area), sev- eral blades were separated from the raft to simulate what happens to the unmarketable eggs-on-kelp product that is discarded and left floating on 456 Peterson — Survival of Herring Eggs on Kelp the surface. These blades were placed in mesh boxes (collapsible crab pots covered with 0.25-inch mesh net) and submerged just under the sur- face (10 cm). Several blades were also attached outside the crab pots for comparison. Kelp condition was monitored every second day during em- bryo development for changes in color, turgidity, and integrity (i.e., still in one piece). A simple scale was used to assess kelp condition in the field (Table 1). Egg condition was assessed in the field according to eye and body pigmentation, movement within the egg casing, and number of body coils around the yolk sac (Stick 1990). When egg condition approached that of hatching, 3-cm2 samples of eggs-on-kelp were collected and pre- served in a solution of 70% ethanol and 30% seawater. Preserved embryos were analyzed and staged following development stages as described for Atlantic herring, Clupea harengus (Jones et al. 1978). Specifically, tail-free stage was identified by tail separation from the yolk and oblong yolk shape, and late embryo stage was identified by comparatively dark eye, head, and body pigmentation and the embryo body coiled around the yolk. Wa- ter temperature was relatively constant throughout the sampling period (Fig. 1)(spawning events 1-4). Salinity fluctuated within sampling periods and decreased throughout the season. Salinity remained relatively con- stant during spawning event 1, decreased during spawning events 2 and 3, and increased after the sixth day of spawning event 4 (Fig. 1). In general, kelp deteriorated under these conditions found in San Fran- cisco Bay, but how quickly kelp condition deteriorated appeared to de- pend on decreases in salinity. The more marked the decrease in salinity, the more accelerated the deterioration of the kelp. For example, during spawning event number 1, salinity remained consistent and the kelp re- mained in fair condition, deteriorating slowly over 20 days. In contrast, during spawning event number 4, salinity decreased sharply at day six, but increased afterward. The kelp continued to deteriorate and by day 20 the kelp was entirely decomposed (Fig. 1). For all four spawning events, eye pigmentation and embryonic move- ment were observed in the field 10 days after the first day of spawning (marked by arrow points, Fig. 2). The condition of the kelp (at the arrow point) ranged from good to fair depending on the spawn sampled. For spawning events 1 and 2, both submerged and floating kelp were in at least fair condition or better 10 days after spawning began (Fig. 2). Kelp placed in the mesh box during spawning event 3 remained in fair condi- tion longer than kelp left suspended. Kelp condition for spawning event 4 was less than fair when the eggs had reached the late embryonic stage (Fig. 2). It is important to note that for all spawning events, kelp remained in fair or better condition for at least 4 days after eggs were noted as having reached the late embryonic stage (Fig. 2). One of the interesting results of this research was that for the more substantial spawns (those with several layers of eggs), kelp condition was not an impediment to egg survival but deterioration among the eggs them- selves contributed to a large percentage of mortality. On blades where Herring: Expectations for a New Millennium 457 Table 1. Kelp condition assessment scale. Kelp condition was assessed every second day during embryo development for changes in color, turgidity, and integrity (strength). Scale Condition 1 Kelp is dark green in color, blades and stipes are firm, stipe holds the weight of the blades, blades do not tear easily (can be “snapped”). 2 Kelp begins to lose some color, becoming more dull green, stipes may be somewhat mushy in texture but still hold weight of blades, blades are firm and ragged on the edges. 3 Kelp is dull is color, stipes break when handled, blades firm, edges more ragged, water spots visible. 4 Kelp color dull and may be light green, stipes break easily and do not hold weight of blades when pulled from water, blades are easily punc- tured with finger, ragged on edges, but still hold together. 5 Kelp color same as above, stripes are mushy, falling apart, and do not hold blade weight, blade wilts when pulled from water, mushy and de- composing. there were areas of higher egg deposition, normal egg development was observed until the late embryonic stage. In several instances, decay devel- oped among some egg clusters and seemed to prevent the late-stage em- bryos from successfully hatching. From observing this on both kelp and pier pilings, I suspect that the underlying layers of eggs may die during development; then, as they begin to decay, contribute to the deterioration of surrounding embryos. Similarly, eggs that became covered with silt and particulate matter would reach the later embryonic stages but fail to successfully hatch. There are several strains of bacteria and/or water molds that are known to colonize fish eggs and organic matter in estuarine wa- ters, and one or both of these processes probably occurs in San Francisco Bay herring eggs-on-kelp. Blades left outside the mesh boxes suffered al- most immediate damage or complete loss due to predation. Suspended blades were not immune to this loss, because similar damage was seen on blades within 4 m of the water’s surface. Several local species of birds were observed actively preying on floating and submerged eggs-on-kelp. The results indicate that under the salinity and temperature condi- tions observed during this sampling period, giant kelp remained an ad- equate substrate for Pacific herring egg development. It should be noted however, that environmental conditions in San Francisco Bay are extremely variable from year to year (California Department of Fish and Game 1997). 458 Peterson — Survival of Herring Eggs on Kelp Spawn no. 1 - January 7, 1999 30 25 Temperature 20 Salinity 15 5-Jan 10 7-Jan 5 0 Celcius/ppt/condition 051015 20 25 30 Spawn no. 2 - January 25, 1999 30 25 Temperature 20 Salinity 15 19-Jan 10 21-Jan 25-Jan 5 Celcius/ppt/condition 0 051015 20 25 30 Spawn no. 3 - February 11, 1999 25 20 Temperature 15 Salinity 10 5-Feb 10-Feb 5 Celcius/ppt/condition 0 0102030 Spawn no. 4 - March 5, 1999 25 20 15 Temperature Salinity 10 4-Mar 5 0 Celcius/ppt/condition 051015 20 25 Days Figure 1. Temperature, salinity, and kelp condition. Kelp condition scored on a scale of 1 (good) to 5 (poor) (Table 1). Dates of spawns represent the first day of a spawning event. Dates within a spawning event refer to date of kelp suspension. Herring: Expectations for a New Millennium 459 Spawn no. 1- Kelp Condition 5 4 3 5-Jan 2 7-Jan Condition 1 0 051015 20 25 30 Spawn no. 2 - Kelp Condition 5 4 19-Jan 3 21-Jan 2 25-Jan Condition 1 BOX 0 01020304050 Spawn no. 3 - Kelp Condition 5 4 5-Feb 3 10-Feb 2 BOX Condition 1 0 0102030 Spawn no. 4 - Kelp Condition 5 4 4-Mar 3 03/11 BOX 2 Condition 1 0 051015 20 25 Days Figure 2. Kelp condition relative to egg stage.