Deployment of standard monitoring units for the recruitment of fishes, SMURFs, in Trinidad Bay, California

Rockfish (genus Sebastes) are ovoviviparous with pelagic larvae that may travel great distances before settling on shallow reefs where they become substrate-dependent juveniles. Artificial reefs can be used to monitor juvenile recruitment by providing settlement habitat. Juvenile recruitment in this context refers to the onshore delivery of juveniles from pelagic larval habitats to nearshore reefs. In this study, submerged artificial reefs, Standard Monitoring Units for the Recruitment of Fishes, SMURFS, were used to examine juvenile rockfish recruitment in northern California. Two SMURFs were deployed in Trinidad Bay, California, between June and September of 2010 and 2011. SMURFs were fished on a weekly basis. The objectives of the study were to 1) determine the effectiveness of using SMURFs to examine juvenile rockfish recruitment in northern California, 2) provide a baseline description of the abundance, diversity and succession of all species sampled, 3) compare the physical oceanographic conditions between 2010 and 2011, and 4) analyze the relationships between rockfish abundance and physical parameters within and between each field season. The SMURFs deployed in Trinidad Bay, California, provided suitable settlement habitat for juvenile fish. In total, nine species of fish, representing five families, recruited to SMURFs over the duration of the study. Species sampled included: northern clingfish (Gobiesox maeandricus), black rockfish (Sebastes melanops), copper rockfish (Sebastes caurinus), redbanded rockfish (Sebastes babcocki), bocaccio (Sebastes paucispinis), kelp greenling (Hexagrammos decagrammus), cabezon (Scorpaenicthyes marmoratus), fluffy sculpin (Oligocottus snyderi), and penpoint gunnel (Apodicthyes falvidus). In addition to these species, it is possible small numbers of gopher rockfish (Sebastes carnatus), and black-and-yellow rockfish (Sebastes chrysomelas), were also sampled. Due to similar juvenile morphologies, these two species were grouped together with copper rockfish and considered the CGBY rockfish complex. The abundance of fish varied between the years with 3,657 fish sampled during 2010, and 471 fish sampled during 2011. The majority of fish collected, 87%, were either CGBY or black rockfish. Fish moved onshore in relation to their parturition date. Inter-annual comparisons were limited due to the short duration of the study. However, 2010 was characterized by having cooler sea surface temperatures. This implies that cooler water temperatures may promote stronger recruitment years. At the same time, no physical parameters were able to describe the within year variation of weekly abundance. Based on this study, it is recommended that Trinidad Bay, California, be used as a site for monitoring juvenile rockfish via SMURFs. Continuing to collect data regarding the recruitment of juveniles to nearshore reefs may improve the accuracy of predicting future adult stock sizes. This could lead to proactive management strategies that can be tailored to local populations. Furthermore, results may also provide a tool to assess the quality of similar habitats designated as Marine Life Protected Areas along the north coast.