The Spring Kodiak Trawl Survey (SKT) has sampled annually since its inception in 2002. The SKT determines the relative abundance and distribution of spawning delta smelt (Hypomesus transpacificus). The SKT samples 40 stations each month from January to May. These 40 stations range from San Pablo Bay upstream to Stockton on the San Joaquin River, Walnut Grove on the Sacramento River, and the Sacramento Deep Water Ship Channel. Each ‘Delta-wide’ survey takes approximately 4 - 5 days per month to complete. Historically, ‘Delta-wide’ surveys were followed by a 'Supplemental’ survey two weeks later to intensively sample areas of highest delta smelt concentration to estimate the proportion of male and female delta smelt that were in pre-spawning, spawning and spent maturation stages. Beginning in 2008, in an effort to minimize take of spawning adults, routine ‘Supplemental’ surveys were discontinued and are now only conducted under the recommendation of the Smelt Working Group and the approval of managers. 'Delta-wide' surveys are numbered consecutively beginning with number 1, and 'Supplemental' surveys are numbered consecutively beginning with number 11.
The kodiak trawl net has mouth dimensions of 25 ft wide x 6 ft high when stretched taught. Net mesh sizes graduate in five sections from 2 inch stretch-mesh at the mouth to 0.25 inch stretch-mesh at the cod-end. A 10 minute surface tow is conducted at each station with 2 boats that spread the net mouth fully open. All fish, shrimp, and jellyfish collected in the tow are identified and enumerated. Delta smelt are further processed to identify gender and maturity. Water temperature, electrical conductivity (specific conductance), Secchi depth, and turbidity are collected at the beginning of each tow.
The U.S. Fish and Wildlife Service’s Biological Opinion for delta smelt has criteria pertaining to delta smelt protection based on SKT Survey results. Those Survey results, provided in near-real time, are used by state and Federal resource managers to assess the risk of entrainment of delta smelt at the Central Valley and State Water projects.