Maxwell et al.: Fishery dynamics of Loligo opalescens 



. 669 



reduced in post-El Nino October or March. A noticeable 

 concentration of fishing effort off the southern shore 

 of Santa Cruz Island was evident in the post-El Nino 

 period, however. The landings data may indicate that 

 this southern shore, represented by blocks 708 and 

 709, was indeed productive. In the pre-El Nino period 

 (1992-96), blocks 708 and 709 represented 3% of the 

 landings in the bight. In the post-El Nino period (1999 

 to early 2000), these two blocks came to represent 12% 

 of the landings. 



The spatial distribution of fishing activity appears to 

 shift over the course of the squid fishing season. In the 

 Southern California Bight, October and March mark 

 the traditional beginning and end of the squid fishing 

 season, respectively (Butler et al., 1999). In the present 

 study, fishing activity along the Santa Rosa and Santa 

 Cruz Islands moved largely to the southern shores by 

 March, leaving the northern shores relatively unfished. 

 This spatial shift may reflect change in local squid 

 habitat or changes in the fishermen's behavior. As a 

 rough indicator of habitat quality, water temperature 

 did not consistently differ between the northern and 

 southern waters around Santa Cruz Island in March 

 and April, both at sea surface and at 75 meters depth. 

 Wind conditions, on the other hand, change consider- 

 ably from October to March. The northern shores of 

 Santa Rosa and Santa Cruz lie on the rim of the San- 

 ta Barbara Channel. Wind speed and wind stress are 

 relatively low through the channel in the fall and early 

 winter but increase significantly in March to remain 

 high throughout the spring and summer (Winant and 

 Dorman, 1997; Harms and Winant, 1998; Dorman and 

 Winant, 2000). It remains unresolved whether the high 

 winds in the Channel in March and April create ocean- 

 floor turbulence and turbidity that discourage squid 

 spawning (cf, Roberts and Sauer, 1994), or whether 

 fishermen simply eschew the rocky Channel in favor of 

 the southern shores of the islands. 



Although satellite remote sensing can generate a 

 "neutral party" record of fishing effort, we note three 

 caveats associated with satellite data. First, large sta- 

 tionary sources of light, such as coastal cities, must be 

 excluded when quantifying fishing vessel activity. The 

 exclusion of urban light sources can result in under- 

 estimating effort, because boats that work near large 

 light sources can be excluded from analysis. We were 

 concerned that an underestimation of effort along the 

 mainland coast would explain this study's post-El Nino 

 increase in LPUE. Landings data, however, may indi- 

 cate that effort in coastal blocks actually declined after 

 the 1997-98 El Nino. Coastal blocks accounted for 19% 

 of the landings in the pre-El Nino years (1992-96), 

 dropping to 11% of landings in the post-El Nino years 

 (1999 to early 2000). 



Second, the spatial resolution of the satellite imag- 

 es may be large enough to allow multiple boats to fit 

 into one "pixel" of detected light. Thus, effort may be 

 underestimated. Analysis of the ground-truthing fly- 

 overs, however, did not indicate a strong interaction 

 between boat aggregation and nightly fleet size. Boats 



may have indeed aggregated over the course of our 

 study, but our analysis indicates that such aggregation 

 was independent of nightly fleet size. In this case, the 

 absolute values of estimated effort and LPUE would be 

 underestimated across all dates. The relative values of 

 effort and LPUE, however, will be only slightly affected 

 within a time series; therefore we place confidence in 

 our examinations of the temporal patterns of the ef- 

 fort-based data. A third caveat is specific to the present 

 study. The ground-truthing work occurred during a pe- 

 riod of relatively low fishing effort (1999-2000). Future 

 fly-overs during periods of greater effort will be useful 

 in corroborating our observed relationship between fly- 

 over and satellite data. 



The present study demonstrates that light detection 

 by satellite remote sensing is useful for examining tem- 

 poral and spatial patterns of fishing effort and popula- 

 tion abundance, as measured by LPUE. Light detection 

 by satellite has certain drawbacks, but these are not 

 insurmountable. Importantly, geo-referenced satellite 

 images provide an independent source of fishing effort, 

 which can be feasibly integrated with environmental 

 data through GIS analysis. With regard to market squid 

 off California, satellite data can help provide fine-scale 

 data on fishing location for this fishery's ongoing man- 

 agement efforts 4 ' 5 (see also Mangel et al., 2002). Al- 

 though mandatory shielding of the boat lights went into 

 effect in May 2000, these lights are still detectable by 

 the satellites (authors' pers. obs.). Recently, effort log- 

 books have become mandatory for squid fishermen off 

 California. This requirement points to a unique oppor- 

 tunity to collect and corroborate fishery-dependent and 

 independent measures of fishing effort. 



Acknowledgments 



We owe much gratitude to personnel of California's 

 Department of Fish and Game for their assistance in 

 the ground-truthing work. In particular, we thank the 

 pilots Jeff Veal and Tom Evans, and the following aerial 

 observers: D. Bergen, T. Bishop, S. Carner, D. Hanan, 

 C. Kong, J. Kraus, A. Lohse, S. MacWilliams, D. Ono, 

 M. Songer, J. Wagner, and E. Wilson. We also thank 

 Paul Crone for collaboration on this project, Chris Reiss 

 for extracting CalCOFI water temperature data. Rich 

 Cosgrove for assistance with mapping, Kevin Hill for 

 information about the Pacific Fisheries Management 

 Council, and George Watters and anonymous review- 

 ers for constructive comments. This project was funded 

 by the California Department of Fish and Game and 

 U.S. Department of Commerce (NOAA NESDIS Ocean 

 Remote Sensing Program). 



4 California Department of Fish and Game. 2003. Draft: 

 Market squid fishery management plan. [Available from: 

 Calif. Dept. Fish Game, 4949 Viewridge Avenue, San Diego, 

 CA 92123.] 



5 Maxwell, M. R., L. D. Jacobson, and R. Conser. Manuscript in 

 review. Eggs-per-recruit model for management of the Cali- 

 fornia market squid (Loligo opalescens) fishery. 



