Age and Growth of Pacific Sardine in California During a Period of Stock Recovery and Geographical Expansion By Emmanis Dorval Jenny McDaniel Southwest Fisheries Science Center Dianna Porzio California Department of Fish and Game

Pacific Sardine Sardinop sagax

Background Patterns of individual fish growth rate After population decline: o Following low population level due to exploitation (or to other events), individual fish growth rate is expected to increase (Le Cren et al. 1972, Botsford 1981). o Following low population level, individual fish growth rate may be several times higher than normal growth rate (i.e., pre-decline or pre-exploitation level ), Le Cren et al. (1972).

Background Patterns of individual fish growth rate After population rebuilding: o Individual fish growth rate is generally expected to decline toward normal growth rate (i.e., pre-decline or pre- exploitation level ). o However, the extent of this decline may depend on the strength of regulating factors that are in play; and/or on how much the environment/habitat of this species been modified compared to pre-decline or pre-exploitation level.

Background Patterns of individual sardine growth rate In the historical fishery ( ): o Length-at-first annulus formation: 101 – 131 mm (Marr 1960) During the recovery of the stock (1990s – 2000s) o Butler et al. (1996) o Hill et al. (2007, 2009, 2011)

Background Patterns of individual sardine growth rate P. sardine growth curve Butler et (1996) Fish samples o Daily Egg Production Method (DEPM): April - May 1994 o Ensenada fishery landings Von Bertallanfy growth model o L ∞ = ± 1.6 o k = 1.19 ± 0.04 o t 0 = 0 (fixed ) Birthdate: January 1

Background Patterns of individual sardine growth rate P. Sardine growth curve Hill et al. (2011) Fish samples o Daily Egg Production Method (DEPM): April – May: o Ensenada/California fishery landings: o Pacific Northwest fishery landings: Birthdate: July 1 L 0.5yr = 114 mm L ∞ = 242 mm k = 0.364

Background Sardine growth rate: current issues o Density -dependent changes in growth rates or reproduction have not been identified nor evaluated (Hill et al. 2011). o Combining fishery-dependent and fishery-independent data may not be the most reliable way to detect density-dependent. o A single growth model is derived in stock assessment model and applied to all fisheries (i.e., Ensenada and/or California, Pacific Northwest). o There are no known aged-fish: it is difficult to estimate age-reading bias and imprecision from multiple readings of otoliths.

Research Objectives Develop methods to estimate and compare growth rates in the California spawning stock: o During the recovery of the stock in California (1980s-1990s). o During the recovery and expansion of the stock from California into the Pacific Northwest and British Columbia (1990s – present). Determine how fish migration and fishing development may affect sardine growth rate in the California spawning stock.

Methods Sample collection o DEPM April survey: o California: San Diego – San Francisco Age estimation o Annual increment from whole otolith, i.e. unpolished otolith, Yaremko (1996) o Birthdate assumption: July 1 o Age-readers: 3

Methods

Methods Growth model o Von Bertalanffy growth model (Beverton and Holt, 1954) o Maximum likelihood estimation of parameters o Mixed-effect model Lt ~ Age | Reader L ∞ (random factor ) k (fixed factor) t 0 (random factor)

Methods Age-1 + sardine biomass Growth comparison between: Year-classes: Year-classes:

Preliminary results Butler et al Least-squares based model (Reader best ages) L ∞ = mm k = 1.19 t 0 = 0 (fixed)

Preliminary results Least-squares based model (Reader best ages) Mixed -effect model Length ~Age | Reader L ∞ =283 mm ± 9 k=0.22 ± 0.01 t 0 = ± 0.5 L ∞ = 328 mm k = 0.14 t 0 = -3.13

Preliminary results Mixed effect model Length ~Age | Reader Mixed -effect model Length ~ Age | Reader L ∞ =263 mm ± 10 k =0.26 ± 0.01 t 0 = -3.11± 0.68 L ∞ =294 mm ± 10 k =0.19 ± 0.01 t 0 = ± 1.31

Summary Compared to previous study, i.e. Butler et al. (1996), sardine growth rate in the spawning stock appears to have decreased. However, early age and growth data may need to be re-analyzed so that comparison can be based on most recent age-reading and statistical methods. Growth rate of sardine in the and in the year-classes are significantly different. However, comparison of these year-classes may need to be based on data that include similar age-classes.

Summary We will continue to age our historical sardine otolith samples to address these concerns. We will include age-reading errors in future models, so that all model assumptions can be met.

Acknowledgement This study is an ongoing research collaboration project between the California Department of Fish and Game (CDFG) and the Southwest Fisheries Science Center (SWFSC). We thank all CDFG staff that participated in the age-reading of sardine otoliths, specially Valerie Taylor. We tank all SWFSC staff that participated in the collection and management of sardine otolith samples, specially Beverly Macewicz.