Ghost fishing is the mortality caused by lost fishing gear and as such, its effect on target populations is difficult to quantify. This study seeks to rectify that by developing a methodology to estimate the effect of ghost fishing by lost pots and traps on large crustaceans (crabs and lobsters). Forty-four case studies, consolidated from published literature on the amount of lost traps and their mortality rates, are used as the basis of the calculations. Missing parameters are inferred from existing values in similar case studies. A Monte Carlo simulation is used to analyze the sensitivity of the results to uncertainties in the input data. The mean estimate of ghost fishing as a percentage of reported landings, over the forty-four case studies, is 3.8%. Ghost fishing is a management issue to contend with, especially in areas where fishing effort is high. Improved legislation on using biodegradable twine and/or Galvanic Time Release mechanisms has and will ameliorate the destructive impact of lost traps on vulnerable ecosystems.